I personally don't know anything but you could try calling your local veterinary offices. Not all vets are going to have much knowledge in aquatic life though and so you might have to call a few different places (or ask if they know someone in particular you can talk to). That would be my best advice.

Define "not swimming right".
Is it swimming with a limp? Or is it swimming sideways like a crab.
Maybe instead of going forwards, it keeps stumbling over and all the other fish in the street turn their heads to look at it
and they go oh my god, and simultaneously gasp, waiting to check if he's okay before moving on. Suffice to say they'd probably forget all about it, three seconds later.

Anyways, the food causing a change in the fish's behaviour is pretty unlikely.
You can tell if this is the case by starving your fish for like, 2 or 3 days, changing it back to its old food won't help you find the root of the problem. So i'd lay off that until you find out.
If it's not the food then it might be disease or infection. At which point i have no idea what to suggest.
And if i remember right from my fish owning days, a sudden change in temperature can also cause it disorientation problems. So if its suddenly become really coldddd, or you moved the tank from a warm place right next to a frosty window... things like that really.
Goldfish aren't exactly complex animals, finding out the issue should be a simple enough task if you just try to think about all the causes it might be.

Good luck with your fisho.
What's its name?!

He is swimming sideways, like... his right side faces the ground, left side faces the top.

The temperature in the tank remains the same at all times due to a heater we have in the tank that helps keep it warm during the colder times of the year. The only real thing that has changed is that they were switched to a different food type three days ago.

I dont tend to name my fish. In fact these poor guys were rescue fish who were used for decoration at a party... Cause you know.. fish that cost less then a buck a piece are for putting in tiny bowls with no air and should be thrown away right after you are done suffocating them in a tiny space.

Yeah it's pretty awful.
I'm almost brought to tears every time i have to deal with a spider, but they are one of my biggest most utter fears.
I apologise lots and lots of times, and i always say "Why do you have to be here, in my space, if you weren't here, i wouldn't have to do anything"
so i do understand your feelings for those goldfishies to an extent.

As i said, just starve them of food for like, 2 days, if nothing changes, then it'll definately be an infection or disease, which would be time to go to a vetenarian.

it may sound odd, but put a couple of frozen peas (do not defrost!) in the tank. It sounds like your fish might have an infection of some sort. A vet friend of mind gave these instructions to another, mutual friend. It sounds weird, but *shrugs* what could it hurt?

I can give it a shot.

Peas without shells mind you, Squeeze the pulp out :3 Also clean the tank in case it's an infection and in the water.

I do not think it is infection. I have goldfish and it happens with mine all the time. They eat alot, and when they come up they swallow alot of air as well. I have 2 very happy floatie fishies. Does your fish float all the time, or just sometimes? Also, how often do you feed them?

I feed them once a day, in the morning, but he was floating weird before he was fed. But he seems to be feeling alright.. perhaps he sucked up a lot of air or was constipated.. Either way I am happy he is much better.

Glad to hear that.

When I had fish, I was told that floatation issues were often caused by over-feeding. Try cutting back a little on portion size for a few days, and see if the problem persists.

This happened to a tinfoil barb of mine once, except he ended up bloating up a ton and floating upside-down at the top. After a day or two, the issue subsided.

It could be from overfeeding or a derp with the swim bladder, but it usually subsides. If the problem persists with dietary change or starvation, I'd say treat him in a separate tank with some melafix since that's typically the "FIX MY FISHY'S WEIRD SICKNESS" remedy of choice.

Also, what kind of food have you been feeding them? This has a lot to do with potential bloat causes. Are you feeding them flakes, pellets, frozen? What kind? Vegetable, bloodworn, shrimp? Do you give them any additional treats such as cucumber or zucchini? Do you have any live plants in your tank?

What's your tank size? What kinds of fish and what sizes are they? Gravel or sand? How often do you clean, and what percentage of a water change do you do? What pH do you keep the tank at?

I have had these guys for well over 6 months and I am pretty routine when it comes to what I do for them. Including regulating the temperature in their tank. I only ever change about 25% of their water, and get the gunk out of the gravel once a month. I keep no living plants in the tank.. Goldfish tend to uproot plants and its just a hassle that ends up killing the plant. I also change their filter on a weekly basis. On top of that we have one bottom feeder fish who gets up the left over food. I know it may seem like I change the filter very frequently, but it gets changed when its dirty.. and its dirty within a week.

The only recent change was the food. I used normal goldfish flakes and treated them to some freeze dried blood worms once a week. I changed their flake food to a different type of flake food over the last three days, so I assume that was the problem. He was showing the problem before his feeding, and the only reason I knew he wasnt dieing was because he had a good appetite in the morning. He was able to make it to the top of the tank, well.. though awkward.. Within about 8 hours or so he is swimming proper again, so in the morning we are going right back to the old flakes.

Errrr my computer derped so my reply is down there. xD

No, with goldfish that's very good care since they produce twice the bio-load of typical freshwater fish.

So, yeah just flakes. I'd try giving them some more variation in their diet, personally. A varied diet will keep them well nutritionally and their little innards working a little better. Most fish LOVE zucchini and cucumber, and some like carrots as well. Lots of fish flakes are made with vegetable, but as it is with humans, processed food is never as good as the real deal. :D Also why I prefer frozen bloodworms over the freeze-dried. Also fish go INSANE over them and it's adorbs.

Glad that he got better and whatnots. It's always... super awkward to deal with a derpy fish.

Is he sinking? If so, it could be a problem with the swim bladder, and you could try making an artificial swim bladder.

He was able to get from top to bottom and swim inbetween... he was really just swimming on his side. But he is better now.

I am glad he made a fall recovery. I love fish in all shape sizes and breeds and colours. I take it there were fan tails or bubble checks or telescopes or common gold fish. I had some amazing and wonderful fish over my life time. But I hope they are doing well. have a nice day be safe Danny.