Negative HPT and USG for pregnancy.

I have normal menstrual cycle of 30-34 days. Last month I was sexually active. On 33rd day, I had bleeding which continued till 34th day late night, had a break of 8 hrs and again continued 6 hrs after which it again stopped. I had a urine pregnancy test which was negative. After 8 hrs of stopping, it again started for merely half hour and then stopped. On 37th day morning i had urine pregnancy test which was again fully negative. The same day I had an whole abdomen ultrasound. The reports showed everything normal except bowel inflammation. The same day after ultrasound(transabdominal), I again started bleeding with bright red blood like periods which continued 4 hrs and again stopped. I am having pelvic pain which was light before first day bleeding started but started increasing slowly. Now the pain is high. Last month I consumed Unwanted - 72 on the expected ovulation day. How long should I keep checking to be conform that I am not pregnant. I don't have any changes in my breast.