TTC...why am i not prego yet?

My husband and I have been TTC for months now with no luck. I have been monitoring my cycles, and for the past 3 months have been using OPK's. We are BDing when Im most fertile and when im not most fertile. We have tried both methods. We have tried every day during fertile time, and every other day because we got advice on both methods. we mostly BD before we go to bed, so i elevate my hips and sometimes fall asleep that way. I have been using prenatals for the past few months as well. This month, im on day 20 right now of my cycle, i have had all negative OPKs. I have been testing twice a day too. I believe I have already O'd because i was montoring my CM, but im not sure. this has never happened. I usually O around day 15-16. This month, I started using the Maca root extract, and I dont know if this is the reason of the negative OPKs, and im not sure if we are doing everything right. Im 25 and i have never been pregnant and so is there something else i need to do to raise our chances? i have been to the doctor for a preconception screening and everything. she cleared me, so am i doing something wrong? Also, have you heard good or bad about maca helping with TTC, and if so, what kind of maca was used?