I would call your doctor and have them do a blood test. Your symptoms seem similar to the ones I had when I had a miscarriage. I had spotty periods 2 months in a row, but each time I took a pregnancy test (I took 4 of them), they came out negative. The day I was going in for tests to figure out why I was having the spotty periods, I miscarried, but didn't know it. The pain was so bad I had to pull over on the highway on the way to my test, and I had serious heavy bleeding. 2 weeks later I rec'd my test results and they showed that I was pregnant, the hcg was just so low the pregnancy test couldn't detect it, therefore, I did have a miscarriage the day I thought. I am also O- and my husband is O+, so I was worried that I hadn't had the RH factor shot within the 72 hr window, but as it turned out, I didn't have any antibodies.