What would a doctor do to check? Will it hurt?

Hi,
Welcome to ehealthforum,
Vaginal bleeding during or after intercourse/masturbation that you describe is not normal and could suggest chances of infection, internal injury/trauma, vault injury, endometriosis, hormonal derangements affecting the bleeding pattern, anemia etc. It is difficult to comment on the exact cause for the abnormal bleeding that you describe without examining you. The exact cause can only be made out after careful evaluation. Visit your doctor/gynecologist at the earliest for thorough examination and further evaluation to look for the underlying cause for the bleeding that you describe and also confirm the hymen rupture. Treatment as indicated (based on examination findings and investigations results) would be started to help you in controlling it. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet. If infective cause is detected, get your partner also treated simultaneously to prevent chances of re-infection.
Take care.