bleeding during intercourse

Hi I'm 32yo female and have had the same partner for 7 years (no childrent) he has had a vasectomy so that I don't need to be on the pill.  In the last 2 years on and off I have had bled quite a bit during sex (bright red in colour)  November 2007 through my local GP and he tested me for thyroid, as well as all VD, STD, HIV Chlamydia etc, everything came back negative.  Bleeding often occurs 2wk before my cycle is due and stops after sex.   We may have sex the next day or a couple of days later and I wont bleed at all, I don't understand why I'd bleed one day and not the next?   I recently got re-tested again (for everything excluding thyroid) at the beginning June 2008 by a different Dr and she did 2 types of smear test as well as the blood tests and again everything came back negative.  My partner hates it when it happens and it generally becomes a passion killer - I am getting very frustrated and becoming somewhat paranoid and reluctant to have sex with my partner.   We do have a very active sex life together and occassionaly a little rough but ironically that doesn't seem to be the times that I bleed.  Any thoughts would be greatly appreciated.

[margypops]

Maybe a tear keeps opening when you have Sex, Has the Doc looked go back ask questions about it , and maybe give it time to heal.