Reason For Absence Of Periods Despite Abdominal Cramping?

Hi, I'm quite concerned. I have had regular 28 day cycles past two month. Prior to that my longest cycle was 32 days. I am approximately 11 days late on cycle day 39. I have had mild cramping in lower abdomen mostly to my right side. This has been last for about almost 2 weeks on and off. I assumed menstrual cycle was around the corner but never came. I usually chart my ovulation and cm but this month was occupied and was not a thought. I took 2 test and both negative. What could be wrong? Also this may be to much info but I have not spotted when wiping or anything but when checking cm. it sometimes has light brown almost beige tint to it.