Feeling the pressure on TTC

In August 2012 I had an unplanned pregnancy, my boyfriend and I were young but we became very excited very fast. In November I was told my unborn child no longer had a heart beat and I had miscarried. We were heart broken and becided to try again.  In January 2013 I got pregnant and am so thinking for my little girl that will be 3 in a few months. But we want more kids. October of 2014 we dicided to start trying again. March of this year I found out I was pregnant again! I cried tears of joy! 7 weeks into the pregnancy I miscarried again. I have  put a lot of pressure on my self about trying to conceive. I want to give my daughter a sibling or really our goal is 4 children altogether. My boyfriend was drinking earlier and got in his feelings about us trying for a baby and how I seem to not be able to get pregnant, and if I do if I can even carry the baby. And questioned if we're meant to be together. He is a great man and an amazing father... I just feel like a failure, like I can't do the one thing a women is supposed to be able to do naturally.