Sometimes I masturbate before I go to sleep at night. Usually nothing is wrong, but sometimes (and this always (link is external) occurs at night, I've found) after I masturbate, a few minutes later I have to urinate. And when I do, it is usually very painful. The feeling doesn't pass either. My scrotum usually gets very tightened up, and there is painful feeling above my crotch. Usually I just sit there, drink some water (link is external) until the feeling goes away. ANY idea what this is?