My penis feels extremely hard when it is just flaccid and there is like a dull feeling in my testicles. The veins are extremely visible; both these symptoms are new- I haven't had it all my life. It gets softer then every time I mastuarbate it goes all hard again for at least a day (it never gets fully soft). Also, there is an area on the foreskin which is red and I can feel what feels like bits of string, but maybe it is something wrong with some blood vessels? There is a similar stringy feeling on the other side but actually on my penis, not my foreskin. Red blood vessels are also visible on my testicles.   I've had these symptoms for about two weeks, they appeared a few days after I had quite rigourous sex. I've had an STD check which came through as all clear.   What is wrong?   Is it serious?