Is this implantation cramping or did I ovulate twice?

This is my first month TTC. I usually have 35 day cycles. My last period was 21MAR. I expected to ovulate around the 19th of APR and started using OPK on cd11 to be safe. On cd15 I experienced cramping and EWCM. On cd16 I didn't have a pos OPK, but it was much higher than the day before. I also started spotting on cd16-cd19 - brownish. Husband and I BD on cd12 and cd17. I umed that maybe I missed ovulation with the OPK and ovulated on cd15. 12 dpo I took a HPG - BFN. On cd26 I experienced light cramping, bloating, a pulling sensation on my right lower abdomen and EWCM. I took another pregnancy test, BFN, and then out of curiousity I took and OPK - it came back positive. I've tested positive on the OPK for the following two days (with EWCM), also. Just to be sure, husband and I BD this morning. I'm just curious as to whether I'm REALLY ovulating twice or it's possible the OPK is picking up HCG the HPT can't.....