Sounds like it might be a vet job to look for underlying issues. I've had these animals fast the better part of a year and not be noticeably weaker. Shedding repeatedly, especially when not feeding, is a pretty good indicator that something else is going on with your snake. Shedding isn't just for growth, it's for healing too, so if he's sloughing multiple times while on an extended fast(and weaker) a vet visit is probably your best option.