My last period was about the 21 of last month. My boyfriend and i had unprotected sex on the 4th of this month. I took the plan b pill within 72 hrs. well i should have started my period about 4 days ago, but since last saturday I have had a light brownish -pink spotting. It lasted two days , and it was a medium light flow, i had to wear a pad. then it just stopped. It started again a day later, but this time it was only when i wiped , but it was getting darker .. I also have lower abdomen and back pain. It starts of light and the gets almost too much to handle. I am still spotting with cramping, and I have started to notice tiny pieces of tissue or clots on the toliet paper. The spotting tsill looks like old blood. I think I am probably pregnant, but i havent taken a test yet. I have been tired , and very moody. What could be happening ?