I'm so upset!

Okay, so, I've been trying to convince for 13 months now. In this time two of my sister in laws have gotten pregnant. (I'm so happy for them.) but it makes me crazy. I feel like I'm doing everything right but nothing is working. I have my vitamins, live a health lot life, have very regular periods, track ovulation, have sex during my ovulation, everything! Ugh. I'm so upset. I just want to be a mommy! What am I not doing? Any suggestions?