Progesterone while TTC


We have been TTC for over 1 year, I went to my MD and had tons of labs drawn. No signs of PCOS but she did say my progesterone was low, in range but low. She wants me to take progesterone orally on days 15-25 of my cycle. I usually ovulate later. Should I wait to take the med until after I get a positive OPK? From what I understand if I take before I ovulate it will completely prevent me from ovulating. Also has anyone every taken this while TTC and had a successful pregnancy? I've never been pregnant nor had any miscarriages! Please help!!! Thank you