Dull aching pain? Not ovulation pain..

My cycles are 29 days and AF is due for me on 2/1, I don't know when I ovulated this month because my strips were all "high" fertility and I think I missed a surge strip. We've been bd every other day regardless just in case. I had ewcm on the days glow said I was fertile (4 of them) but today I noticed I'm having a full aching pain on the right side of my lower abdomen. It's too late for ovulation and I took a wofondos test and it was negative. Any idea what this is??