late period, always irregular..

i know i should probably mark it down when i start n end, but i cant remember how many weeks or whatever its been since my last START date.. i kno it was once around the 14th, then the next time i didnt start til the end of the month around the 25-26, then i ended at the beginning of july, but i never started in july, i figured id start at the beginning of august, but i still havent.. ive already taken 3 different tests not at the same time of course, but they all came out negative.. and ive been getting cramps or sharp pains but im not spotting or starting, n im getting all MY period symptoms that i always get before i start, it just seems like its very very late, and i feel like its not starting cuz i keep thinking maybe the tests were wrong, but ive skipped a month before so im just being paranoid kinda, but i was just wondering if anyone has ever had a similar situation going on with them.. im sure it happens to many women n like i said ive skipped a month before but that was about 3 yrs ago.. im always irregular so thats normal but i just cant remember my last start date or end date.. thanks for your time