Possibility of ectopic pregnancy. It?

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. Same day I had ultrasound whole abdominal which showed everything normal except bowel inflammation. After ultrasound I again had bleeding for 4 hrs like periods. I started having slight pain in my pelvic area before few days of bleeding started but it increased too much till now. 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. Is there chances of ectopic pregnancy? If so, how to detect it?