Excruciating lower abdominal/rectal cramps

Hi there! I've been using Glow for about 10 months but have never posted. My husband and I are TTC. I'm 27 and I have a very regular 27 day cycle, ovulation occurring between days 10-12. The past two months I've had an issue that I could really use your advice about. On CD 16 last month and CD 21 this month (today), I had an episode of excruciating lower abdominal pain and rectal pain for 5-10 minutes. It feels like nightmarish, extreme period cramps, plus a pulling/stabbing feeling in the rectal area. The first time it happened was after peeing after sex and the second time was after a bm. (Sorry TMI.) It is like a 9 out of 10 on the pain scale. Today I took an Aleve and it went away gradually but left me exhausted and nauseated with no appetite. There was an early episode like this come to think of it maybe 5 months ago, and that first time it was accompanied by brown spotting with some minimal clots. Any advice about what this could be is greatly appreciated!