I took clomid to help regulate my cycles and it did bring my O date forward from around cd21 to a more reasonable cd14-16. I had poor folicular recruitment and the clomid was prescribes to encourage more folicles. So I took clomid cd2-6 and was recommended to DTD every second day from cd10-cd20 to try and cover it. I always got a BT on CD21 to check for progesterone, and was always good, indicating o had occurred. I also used OPK's and found them to be reliable, testing daily from CD10 till I got a positive.
Was your BT to check for an LH surge or for p4 levels?
Good luck with it.