The nurse is correct you may need more than 50mg to ovulate on day 14. I took 50mg and had unregular cycles of 28, 30, 35 etc, and I tended to ovulate around day 20 on clomid. Thats not true re false positives for OPKs on clomid. My FS said so, I got a OPK positive and it was correct and we were lucky and conceived Julia. We too started DTD from day 8 to day 22 to cover all bases (every 2nd day).

It also depends when you take the Clomid too, I took it on day 2 to day 6 and still ovulated late.

Best wishes and good luck!