Have you had a vet look at it, yet? That's probably your best bet. The vet can take scrapings and run other tests to figure out what's causing the problem.
Hope it's nothing too difficult to clear up
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."