Growth in uterus size but negative HPT.

I had an pelvic ultrasound 2 months ago. That time I had an medical abortion 19 days before. The size of uterus then was 6.0 cm × 2.6 cm × 3.1 cm. After that I had normal periods. After that I was sexually active. I usually have normal cycle of 30-34 days. On due ovulation day, I took unwanted - 72. On 33rd day of cycle, I started having bleeding like a normal periods but it stopped after 36 hrs. It again started after break of 8 hrs which continued for 6 hrs which stopped for 8 hrs again and then again continued for half hour. Till 37th day morning I had two urine pregnancy test which was negative. Same day evening I had an ultrasound where nothing was found and everything was normal but uterus size was 6.353 cm × 2.867 cm × 4.113 cm. After ultrasound I again had bleeding for 4 hrs which was like normal periods. I am having pain in my lower abdomen but nothing is found in ultrasound. Size of my uterus has increased. Does this mean I am pregnant? Can this also be ectopic pregnancy?