The snake looks pretty young, those brown spots could be from the healing umbilicus (belly button) on your snake. Which is completely normal.
If you aren't regulating your UTH with a thermostat (note: not a thermometer) then this could be a burn. When you say there is a pink belly, and the belly scales are flaking off, that leads me to believe it is a burn. A pink belly is also the first sign of an impending shed, but the skin doesn't come off until much later. When it does come off, it should be in one full piece.
Could you move the probe that is over the heat pad under the substrate and tell us what it reads?
Looking forward to the picture.