Provera and Ovulation

I was just wondering if this has happened to anyone else.... I had an erratic period that was on and off the last wk of jan and the first wk of feb. I was 5 weeks late for my period so I went to my doctor for a pregnancy test. The results were negative, to my dismay. My doc put me on provera because I had such regular periods for years. I had a spike in my temp this morning and I checked my cervix which was def SHOW. I read that you aren't suppose to do a OPK from 10 am-6pm. I took mine at 1:30 and it was def positive. I called my doc and she said that it was very unusual to ovulate while on provera but not impossible. Has anyone else had this happen to them?