well, im 17 and i have had on and off periods since i was 14 they come probably every three to two months. I had unprotected sex, on the 3rd of august, 3 days after my last period, 7 or 8 days later i had brown discharge and light spotting for two days, i looked it up and everything pointed to implantation bleeding . Well i waited a week and everyone was telling me to take a test but im not due for my period untill the 22 or 24, they both came out negative, so , what could the problem be, why did i have that brown discharge and spotting? could i still possibly be pregant?