[cypher]

What kind of wheel do you have & what size is it? It sounds as though he could possibly be rubbing against the spindle in the wheel?
It could be he's rubbing against something else in the cage too, it's always a good idea to check things from time to time to make sure nothing has rough edges that could be a problem.
If you can get a photo that might help see what's going on.

AxisOkami mineral stones aren't good for them & it's best not to give extra vitamins as most hamster mixes will already have vitamins added & they can end up getting too much of some things which can be harmful.
If it is diet related hair loss usually responds well to a few extra flaxseeds & if needed evening primrose oil & sometimes a little brewers yeast can help too.