So I Was Supposed To Have My Period Of Sept.10th

so i was supposed to have my period of sept.10th and started bleeding mon. 12th and stopped that thurs. 15th. wasnt my usual period cramping so im thinking it was implantation but not for sure and we are trying to get pregnant in august when i figured it up with my fertile days and had sex those days. but my tests are coming back negative. with my other 2 pregnancies i never had this problem. so my questiong is, do you think im pregnant ? i have the signs of swollen boobs, nauesous, and jus not myself.