What Causes Delayed Pregnancy Despite Taking TTC Treatment?

Hi, I m 36 and DH 40. DS 5 yr old, also underwent one abortion few years back. we have been doing TTC since last 3 months. No luck. This time underwent follicular study, showed ovulation on D15. Follicle size was 22.5 mm & endo at 9.5 mm trilaminar. But on the day15, Gynaec said your endo still shows trilaminar and pattern which she usually observes when progesteron hits on is not evident in my case, so she suggested MyProg200 to be continued for next 15 days. Then run Pregnancy test, if positive then to see her otherwise terminate taking myprog and try for next cycle. Are we on right track? If i have not take any medication for egg rupture etc, do i still need to go for myprog? My cycles are healthy otherwise. Have had no issues with any pregnancies before. Your opinions are most welcome.