spots in my undies

anyone..i cannot figure this out, recently when i've been wearing my tighty whities all day, i notice that there are small dots on them..kind of like flea dirt from a cat..I have no rash, no pain, no redness, nothing i feel and look perfectly normal. but every day the spots are there and do not come out in the wash..I wore a brand new pair of underwear yesterday, the spots where there at the end of the day again, I chaned to a white towel, just to make sure it wasnt coming from the towel...i dont know..help..