Black Blood clots- What could be the problem?

2 weeks ago I did a pregnancy test which was positive.. after 4 days it turned neg. I did another test the same day and it positive and the same ting happened where when I looked at it 2 days later it read neg. A few days after the 2nd preg. test my period supposedly came. When it came there were dark red clots and I thought I had a miscarriage. Its been a week since my "period" came and its been irregular. Blood comes down every now and then like spots and the blood is black and thick. I have pain in my abdomen and if I stretch my belly feels like I tore a muscle durin sudden movements. I am very worried because the liquid is choclate brown and it is in the form of spotting or clots. Help?!!! Is this normal? What could be happening?