I think all artists reach this low moments, then suddenly you get up high again, then when you question yourself and your skill again youll be in the low again. I think thats the sign your improving! You said it urself,your doing this because its fun so keep drawing ( in my experience, everytime i draw my anxieties, doubts, fears, you forget them, thats why you should draw when ur in a low state)
i recommend you to watch the documentary about takehiko inoue (creator of slam dunk, real and vagabond) my hero. Youl find a lot of things there, especially intimate ones, including his art blocked days, days when he cant draw a page for that week, hell! Even his 1 year hiatus!