Does my Ball Python has a healthy environment?

I am a new owner of a 1 1/2 year old ball python. He is about 3' 2" long and 2" on his widest part. I've had him since August of this year. The closest vet that will accept him is about an hour away. I have a few health questions. I have noticed he has been "yawning" a lot lately. He has also had his head postioned vertically for long periods of time throughout the day. Could these be a sign of a respiratory infection? I feed him a small rat once every three weeks. Is that too long of a wait for him? A few of his scales on his underside have appeared to be chipped. He has a couple of scales on his head that look kind of like a scab. It's nothing huge; I believe that it might just be old shed. Is that right? His temperatures are 85-90 on the hot side and 75-80 on the cool side. His humidity jumps anywhere from 40 to 50 on average. I've been using Aspen bedding. Do you recommend something different or something that holds humidity better? I have three different hides in his enclosure and he hardly goes in any of them! His eating response is great, but today when I fed him he bit himself on accident. I didn't see a wound of any kind. Why did he do that? I just want the best for my little guy.

I'm new to this, but I would say 3 weeks is a little far apart for feedings. It would also help to include a photo of the scab, since nobody will be able to tell you what it is without seeing it. I will suggest a vet visit though if I were you. Better to err on the side of caution if you think that something is actually wrong in my opinion.

That does sound like RI symptoms. "Stargazing" is what it's called when they hold their heads up like that regularly. Get him to that vet ASAP, better safe than sorry. For now, I would bump his hot side temp to 92 and keep the ambients above 80.

Your humidity sounds good by numbers, and if he's shedding fine then it's obviously not too low. What are you measuring humidity with?

And PeanutButler is right that 3 weeks is a while to wait in between feeds. Nothing dangerous but they are generally supposed to eat once every 1 week or 1.5 weeks.

Does he have even a little bit of a wobble? Some snakes have a genetic issue that throws off their coordination/balance, that's what wobble is. It's the only thing I can think of, short of neurological damage, that would explain him biting himself while feeding.