What Causes Delay In Menstruation And Stomach Cramps?

hi, my last proper period was 27th June. i'm a regular 30 day circle. 27th july came and went. the day i was due to come on i started having stomach cramps, this continued for a week until i started spotting. i did not need to use anything the bleed was that light (half day red and a day brown) then the cramps carried on. my breasts are slight sore but it comes and goes. i am a very happy person in a loving long term relationship. everything has just fell into place, i felt more relaxed than i ever have been until missing my period. now i have missed another period and the cramps are still there! i have taken pregnancy tests every week since my first missed peiord and they come up negative. i was constipation for about 3 weeks after my first missed period but now everything is fine. the cramps started off in the ovary area then moved up higher, now they are just left of my belly button. in the ten years since i've had my period i have never missed one. i still think im pregnant as a couple of my friends didnt find out until 11 weeks gone.



my doctor asked my to do an STD which i know will be clear as my partner and i was tested before and were clear. but they do not seem to be bother as the pain is not constant. can you please tell me any possiblities that are causing my missed periods and on off stomach cramps??