Well, it depends on when you ended your last masturbation time. If it happened rightbefore bed, then it could just be some semen stayed in your penis until you woke up. This could also be because you are having a wet dream, especially if you sleep on your stomach (which would make sense, since you masturbate while laying prone on your stomach).
I would say that give it a little time, about 4 days, and if it doesn't clear until then, see a doctor. But this doesn't sound like an STD, infection, or anything to me.
well i am not a guy. but guys can get yeast in fections and other types. reasearch diffrent typs of infections or dial a nurse, some areas have 24/7 dial a nurse or other things like IM a nurse.