to TSB.
The diet you listed is very high in sugar. Is this all your guy eats? If so, he needs some leafy greens like baby kale, endive, escarole, radicchio, arugula, romaine, watercress, bok choy added to his diet. Also good for them is broccoli, cauliflower and hard squashes like acorn and butternut instead of sweet potato all the time. Mushrooms are an excellent source of vitamin D which helps them assimilate the calcium. The Henrys block is great, but a varied diet is essential for a captive squirrel to get the nutrients it needs.
Dried out marrow bones, clean sea shells and antlers are also good sources of natural calcium and help trim the teeth as well.
Your boy may be shedding a winter coat or molting. Hair loss can also be associated with a poor diet. Can you post a picture of your boy?