Some major details about your viv set-yp, etc would greatly help. The first things that come to mind that may cause peeling skin on the belly that isn't due to shedding are either a burn (PLEASE tell me you don't have a hot rock in your snake's viv) or an infection perhaps caused by too moist substrate. A burn doesn't have to be deep, just the equivalent of a sunburn to cause peeling, and if your snake spilled it's water and you just haven't noticed it for couple of days (I have two males that routinely create a swamp in their vivs when I'm not looking), that could also cause a problem. In either case, a trip to the vet is probably in order.