Sarah, I had the exact same issue as you... no AF, and unable to be sure when I ovulated. My doctor did progesterone to clomid, which apparently is a common thing. She gave me to until July 1st to start, and when it did not I took the progesterone for the next 10 days. On Day 11 AF arrived, and then I was able to start clomid.
I think the progesterone helped regulate my cycle, because I had no issues with AF starting after the progesterone. Pregnant on the 3rd round of clomid.
I am 35, btw.
Good luck to you!