From the symptoms you've described it sounds like its getting pretty severe. It's either ri or mouth rot most likely. You really need to take him to a vet. It's probably going to be around $50.00 for a culture and injections. If u wait longer sometimes they need double the meds so it gets more expensive. Not trying to be rude but if u can't afford that, you may seriously want to consider adopting out to someone who can provide vet care if needed.

Overall, while you decide what to do, I would bump the temps up a few degrees and make sure it's super clean. I'd suggest putting him on paper towels to make sure it's really clean.