A good rule of thumb to tell if you’re feeding the right side is either: feed a prey item which is either the same size or slightly larger than the widest part of the BPs body or feed a prey item that is 10-15% of the BPs body weight. I prefer to use the latter as I weigh my BP before going to the pet shop, as where I buy my (frozen) rats from they have the weight range listed on the packet, so I know if I’m buying the right weight. It is possible that the prey items might be slightly too small and thus the snake isn’t growing much, resulting in not shedding very often. Of course, if he hasn’t been eating often this would cause the same problem. Hopefully now that you have bumped the temps up he will eat more regularly for you
(I realise I’ve just assumed that you don’t know how to tell if you’re feeding the right prey size but I just thought I’d check as this was why my BP wasn’t pooping/growing properly when I first got him due to misinformation I received.)