Constant anal bleeding. weeks at a time. but when i have anal sex it goes away for a while. is there an explanation? coincidence? how can i stop it?

Rectal bleeding: I think it is a coincidence that it goes away with sex. Any persistent bleeding like this needs to be evaluated. There are a number of reasons this could be occurring among them are trauma, hemorrhoids, warts, some other type of mass. Even though you are only 19 and it would be very unusual with persistent bleeding you even need to consider cancer as a cause.

See your PCP: Constant anal bleeding for weeks at a time requires further workup. It could be due to trauma from anal sex, but you will likely need some blood work to see if you require a transfusion and you might also receive a sigmoidoscopy or colonscopy so your doc can get a closer look to see if you something serious is going on.