I'm not making enough to live off of if I was living by myself right now either.
In reality, I'd probably be homeless. So... in order to live as just an artist.
I'd say maybe $7,500-10,000 a month just to get by now-a-days.
I'm not 100% on that but that's what it feels like at times.

The harsh truth is that not many artists can legitimately earn a living wage from their work. Some certainly do, so it's not a hopeless endeavor, but just temper your enthusiasm with a bit of pragmatism and know when to admit that maybe being a freelance artist isn't in the cards for you.

That being said, whether you can make a living or not with your work depends partly on yourself and partly on your audience.
Boiling it down to a single sentence: You need to be able to create a product that customers are willing to buy.

You've already done well when it comes to getting your art out there. People have a fairly good idea of what they can expect from you. The next step is proving that you can provide that same quality reliably.
Taking frequent and long haitus', or delivering a lower quality product after a long delay will signal to potential buyers that you might not be interested in their business. Or that they'll have to wait a long time for a product that they likely paid in advance for. If you prove to be unreliable as a vendor, then your business will dry up.

You have to be professional, even when your customers aren't. Remember, you're trying to run a business and you represent your brand. If you are rude, unprofessional and stodgy, then you are going to aggravate and drive off your customers. Try your best to shake off the rude and trollish detractors, but also avoid letting yourself be affected by yes-men and overly enthusiastic flatterers.
Your art is good, but you are not so good that you are immune from critique or faultless in your artistic direction. You may find that customers ask for things that you know won't look good or will take away from what you feel works best for the piece. This is hard - but try not to take such critique personally. If they were the artist, they wouldn't be paying you to do it. You can explain your reasoning, but in the end, the customer is the one paying you. You agreed to take their business and their satisfaction should be your priority.

This leads into having rules and guidelines. Many artists already have Terms of Service which outline what they will or will not do, how they accept payment, set prices and so forth. These guidelines are how you protect yourself as an artist as well as give the customer all the information they need in how to interact with you as an artist/business owner.
If you don't want to do sexual scenes, or have to do heavy revisions after a certain stage, then this is where you say it. Before any money has changed hands, you get to make clear where your boundaries are. If your customer has an issue with where you draw the line, then this is where they should say so. If there is any dispute, you should settle it before agreeing to take the job. Ultimately, you make the decision on whether to take the job or not, but if you do, then you should hold to it, even if you change your mind later. After all, you are making a contract with your customer who is employing you for a short-term project, and you've made it your obligation to complete it (otherwise you probably shouldn't be taking commissions).
If the customer decides to change the terms after the original agreement (such as paying less than what was agreed because they are unhappy with the outcome), then you can hold the contract to them and remind them that your guidelines were already agreed upon. This is where the TOS protects you. If you previously explained that you don't do guro and the customer suddenly demands it, you can refuse them with a clean conscience because it's already clearly listed in the TOS that they should have already agreed to.

Now comes what I feel is the most important part of being a "professional" artist - communicating with your customers.
For many people, this seems to be the hardest thing (artists and commissioners alike). Maybe it's ego, or entitlement or just bad manners, but there are a lot of people that just don't know how to communicate with the person they are working with.
From commissioners that think that good art only takes a few minutes to make, to artists who resent and belittle the people paying them for work, both sides need to understand that they share a responsibility to cooperate and communicate or else neither will be happy with what they get.
A lot of artists burn out on doing commissions because they don't know how or when to say "No", and many commissioners feel like because they are paying the artist, they deserve the artist's undivided attention and every iota of their skill at a minuscule and unlivable price.
Many commissioners also become jaded and resentful of artists for restrictive rules, high prices that aren't reflected in the quality of the work and bad attitudes from artists who should know better than to disrespect the people who are paying them to live.
Artists should know how to speak to their customers as people. Be professional, be understanding and willing to compromise, but don't sell yourself short or give into threats like "I'll report you to Artist's Beware".
Some commissioners can be real bastards and some artists can be real divas. Try to be aware of where on the spectrum you are, and don't forget that you are representing a business - even if it's just you. Especially if it's just you...as there will be no one else to do damage control if you go on a tirade.

TL;DR: You are trying to run your art as a business. Treat it like one. But remember that the people who are paying for your work can take their money elsewhere if you mistreat them.

To put it shortest, per dawnchapel (I forgot how to do the usericon thing, but he's on FA), commissions are a significant amount of work for less reward; where prints you can sell three times ("original", prints, artbook), commissions are basically sold one time (unless you manage to get a commission for your own IP and thus resale rights).

So while I personally find commissions cool, it's sort of disappointing when I can't also just buy some prints of some kind, which support you the artist with much less work on your part.