what can this mean?

ok.im 19 my periods are mostly always the same i have them say the 26th of one month and the following i have it one day before which is the 25th. my last period was on august 25th, it usualy lasts 6-7 days. i had unprotected sex agust 26th, then the 1st or so of september. then again on the 22nd and 29th. is it possible that i could have gotten pg with these dates? i was supposte to get my period on the 24th of september but up to now i havnt gotten anything. i already took two tests 1 this morning and 1 two days before but both were negative. for the past week ive had syptoms but nothing. ive also have had cramps like if i was geting my period only they dont hurt much. is it to early to test? what can this mean?