Need Answers!

I took several pregnancy test two weeks ago and tested positive.  I wasn't due to start my period for another 4 days but was having bad nausea and other pregency symptoms. A week later my symptoms dissapead completely (I was not only having morning sickness but ALL day sickness) I also noticed brown very light spotting which continued for 6 days. On the 7th day I got really bad cramps and the spotting became a little heavier (still dark brown) and I noticed two dime size clots. I didn't have any spotting or clots through the night but the next day had very little brown spotting and another dime size clot.  I took a pregency test and it still shows positive but I've had consistant cramping. Has anyone experienced this? Am I having a miscarriage?