So I normally start my menstual cycle on the 26th and have a light to moderate flow lasting 5-6 days. I had no period in October so I took a pregnancy test result was negative, come December 5 still no period so I went to a near by pregnancy center onDecember 10 for a more accurate test, results still came back negative. I then started my period 2 days later on the 12th and lasted til the 16th. My boyfriend and I have been having unprotected sex regularly for over a year (not trying to conceive but not trying to prevent it either). Yesterday we had sex and I nearly had to stop due to cramping Accompanied by nausea and back pain. Then about an hour ago I went to restroom and when I wiped I had abnormally bright blood also thinner than normal . Does not seem to be heavy flow but I am quite concerned about what is going on.