What Do Missed Menstrual Bleeding And Negative Pregnancy Test Result Indicate?

Hi, im 74days late for menses, tested on day 60, was neg and tested again 1 week after, still neg, i have appointment with the gynae next week. i have encountered a 1 mnth missed period before but the next mnth i will come my mense so i didnt bother much..but this time round almost 3mnths. my first day of my last mense was 14th may 2016, in jul, i encountered stomach discomfort..was not only at lower abd..but was all over my tummy, had backached as well and so does my mood was really bad, eating wise was way humongous then the usual when im getting my menses. What could be my problem?