For some reason I bleed while I masturbate. What. Could be wrong with my vagina?

Masturbation. It is very hard to precisely confirm a diagnosis, so you should see a Gynecologist for pelvic exam, These are some reason for bleeding with Masturbation: 1- trauma to cervix or vagina 2- Infection with Chlamydia/Gonorrhea 3- Inflamed vagina 4- mass in cervix.
It is more likely. coming from the muscular contractions of the uterus causing small blood vessels to rupture. Usually not a problem.