If you masturbate without a lube or just masturbate alot, or masturbate 'hard' (or really pump at it) then it gets dry down there. I usually masturbate 4 times a day regularly, but I wait a few hours (or half hours
) between sessions.
I think it was just irritated down there. Use lube or wait a little while between times you masturbate or be a little bit softer on it. You shouldn't have any problem. =]