Snakes do what makes them comfortable. I've often noticed how my BP is a lot more active for two or three days after i've fed her. BPs are also notorious escape artists, usually trying to find a way out. I remember once i almost lost her inside my car because she found a hole near the steering column i didn't even know existed. It's why 99.9% of people will suggest getting a cage that can be locked.

As far as what's crawling over him... There's really no way to tell unless you catch one and look at it under a microscope. The vet i take my BP to gave me some slides when i first got her and noticed she had mites. I suggest doing something similar, because it could be a big problem if you don't get it looked at right away.