What Causes Vaginal Bleeding Post Intercourse?

hi I bleed the last 5 times my husband and I had sex within the last 2 months, I started about 4 week ago with pressure like i had an infection my dr gave me antib for a week took them all now for the last 4 days i have pressure and back ache could this still be an infection or something else had urine test done today and preg test both were neg can u give me any idea what it might be YYYY@YYYY