We have had our ball python for just over a year, William is about 15 months old. He is approx. 3 feet long, in a 36x18" terrarium, temps are approx 85F during the day, 75F at night. Has an under heating pad on the one side, two hide outs, humidity level is around 45%, when he is going to shed we get it elevated to approx 70%.
When we first got him we were feeding him FT rat pups, we moved onto FT small rats with no problems. He seemed hungry about 4 days after a feed, casing the tank a lot more than usual. I tied a string around the thickest part of his body and the circumference measured bigger than a medium size rat. We have tried giving him the medium size 2 weeks in a row and he is not interested. He almost seems scared of it. We feed him in his enclosure at night, we do not handle him the day of his feed.

Should we just move back to smalls?
Should we wait another week before trying again. It has been two weeks since he's eaten.

Any advice, suggestions would be great!
Thanks
Debra