I'd definitely say you're undercharging judging on your art, but I can't really help with that adjustment, I'm not good with pricing.

seems on the low yea but really depends on how long its taking u to DO a comm. u dont wanna be working 5 pounds an hour u kno?

Alright, I'm not going to say whether or not it is undercharging or not yet as I'm unsure of how long you work. Your work seems really nice, and there's no real answer on whether or not you are overcharging or undercharging, it is all based on people's preference, and you can't please everyone.

If you are working longer than 3 hours on these, I feel like it should be a bit higher. If you are working less than 3 hours, I feel it's around a good price.
If you are working on it for longer, try to figure out a good price increase. If it is higher than 3 hours, I feel like you should charge a bit more. You don't wanna overwork yourself for just a little bit of money. I'd say, if you are working on it for around 5 hours, increase the prices by at least 5-10$. Make two variations of charging, a shaded and nonshaded variant with a price increase for the shaded variant. Maybe around 4-10$ on how the shading is.
All in all, you want to balance time with pay. If you feel you are undercharging or overcharging, look at a hourly pay and figure out how long your average piece takes. And then charge that much. I think the pieces I've seen are at least around 30-40$. And other artists create pieces around your level of quality for around 60-80$.
You, in the end, choose whether or not you undercharging or overcharging. Just try not to burn yourself out, and make sure that you don't take in too much at one time. Limit yourself to around 2-3 pieces at the most at one time. You burn yourself out, and things will become more difficult.

I personally feel your commission prices are decent at their current price. I recommend increasing them at a later time, but as of now, it feels good at this area. I say this as Euros increase the price by a little for those paying in USD. A commission labeled as $20 in price came out to $26.38 due to conversion fees and the like.

This means that increasing your prices by a small amount will be a lot bigger for those paying in USD. This would also make it tricky to introduce your commissions to those who interested should the bar is raised too high.

My only recommendation would be varying prices based on the quality such as Sketch, Flat, Shaded, etc. Otherwise, I see no undercharging at all.

Hmm well for now low prices are good, they draw people in then you can increase.
20 dollars are a bit low for this quality, I'd say you could charge atleast 25. Your lines are on point, you also have a unique style cute style perfect for pokemons.

I have looked at amy artis's pages to find the best price/value and I can confidently say you can raise prices atleast 5 dollars and you'll still have great prices :3