Dr. Said I'm fine. What's going on?

Brit

Hey ladies! So with my ex boyfriend we were TTC for 2 years. I had 2 losses. Then when I was 17 I ended up having a loss as well. I'm currently TTC with my boyfriend and AF just keeps coming. I had some issues with extreme cramping and other things after my last miscarriage. My doctor checked everything out and said everything looked perfect. Could there be something they couldn't have seen on a vaginal ultrasound? Why can't I get pregnant or keep the baby?😔