I had unprotected sex 3 days ago, and i'm bleeding brown blood and have belly cramps and headaches almost all day. he pre cummed inside me? pregnant?

You can not tell: at this moment if you are pregnant. Your bleeding could be due to trauma to the vaginal wall from sex or it is an infection including std. See your doctor.

Not sure: You will not be able to confirm pregnancy until you are late for your period. My concern at this time is that you may have a SEXUALLY TRANSMITTED DISEASE. I suggest you see a doctor for evaluation. You will need a vaginal culture and pelvic ultrasound.