Ironically enough,... AF paid her visit today! Just late in arriving!
Yes, that happened to me 2 cycles ago. I was taking Femara and confirmed O by BBT. My RE had me come in for a u/s and found 2 cysts that were preventing AF from coming. It doesn't happen a lot, but it does happen. The RE said my BBT continued to stay high because the cysts were releasing progesterone. It took 18 more days (after 18DPO) for AF to come. Had she not, the RE said she was going to do something to make her come, but we never got that far.
So, if you can, I would ask your RE to look for cysts to see if that is what is going on. I'd be slightly leary of starting Clomid until you know what is going on.