What Causes Delayed Periods With Sharp Abdominal Cramps?

Hi, I am a 28 year old female.. I have a 32 to 37 day cycle but today is day 39 and I still have not got my periods.. Usually I have very bad menstrual cramps.. I have been having sharp stomach ache and back ache dry similar to what I usually get before periods.. i have been trying to conceive for 8 months.. I don t understand why I have the sharp unbearable stomach aches but still have not got my periods