Afther sex I bleed why?

Make an appointment. There are a number of possibilities. Most are not dangerous: vaginal/cervical lacerations, bacterial infections, cervical/endometrial polyps, etc. Others may be more serious: cervical cancer, endometrial hyperplasia or cancer, etc... See your doctor soon. An exam and few simple diagnostic tests will likely give you an answer.
Bleedinf after sex. If you bleed from the vagina everytime you have sex, you need to see your gynecologist and have examination and find out the cause.There has got to be a source of bleeding.