What is going on with my period!?

Ok, I have a question... I haven't had a period since July 25th! Now, in the end of July and beginning of August I probably had sex 3 times and only once unprotected... Then like a week before my period should have started me and my boyfriend started having unprotected sex everyday... WELL my period never came... I did bleed two times after sex around the day my period should have came BUT it wasn't even enough to cover a panty liner... So I had tried taking a pregnancy test and it said no... Well once I was like 2-3 weeks late I took a couple more... They still said no... Now here we are September 29th and I still haven't had a period... I should have started on the 24th... I took a few more tests which all said no except there was 1 test that looks to have a very faint plus line... I took that one on Friday and since then have taken 2 more which both came up no... So I'm just confused... What do you think could be the problem?

I was thinking maybe it was because I started having sex on a regular basis or stress that it pushed it back a lil bit but now I have missed a whole period and am at least 5 days late for the next one... And I haven't had sex since September 4th... So I don't understand why the hell I haven't either started my period or had a positive test besides that one with the very faint line...