Again, not a doc, but I doubt any internal gastrointestinal issue is going to manifest this way.

Washing it with an antifungal shampoo may help too, but it would have to be in addition to other treatments, because the OTC shampoos are pretty weak. You can get a stronger shampoo, but again it’s a prescription. When you see a doc at some point, bring a list of what you need to talk about, bc you can get the Rx for a shampoo and a cream with refills at the same time, in addition to any other minor things you need, e.g. prescription strength antiperspirant