Hi, im 21 and ive recently lost my virginity. My period is now nearly 3 weeks late and ive experienced brown discharge, lower back pain and stomach cramps altogether they come and go. However ive taken 4 pregnancy tests and they all came back negative. Another thing is that i took a prior to my previous period which i had, i had a blood test and it came back with high levels of progesterone, so i was told it was either due to pregnancy or stress so i took the test at the doctors and came back negative, assuming it was due to stress since it was exam period. Is there any particular reason my period is late?