i'm 18 and I'm sexually active. i had sex feb, 19th. I was suppose to get my period march 10th but it didn't come until today march 19th. it's 9 days late. But now my period is extremely light. That's completely unusual for me because i usually have a normal period sometimes heavy and i cramp, i'm not cramping at all. i also took a pregnancy test march 12th it was negative. Could i be pregnant even if the test was negative?