my last period was on september 20, well me and my boyfriend had sex on the 2nd of october, the next day i had a pain like i was ovulating, wasnt sure though, well i was due for my period like the 18 or 19 of october, and on the 18th i only spotted a little brownish, and the same thing for the 19, 20, and 21st, still no period, i did take a pregnacy test to confirm, 1 yesterday and 1 this morning the 21st, they both came out negative, so what could be going on, my periods are usually on time and very crampy, so i know this is not a normal period, what could it be??