i just dont understand whats wrong with me...

So when me and my fiancé first got together we immediately fell pregnant. We were happy and we fell more in love with each other. Well at 7 weeks we miscarried our baby. I was devastated, I had prematurely bought baby clothes and gotten excited so I did the only thing that helped me cope. Which was laying the babies onesie on my chest at night and a baby blanket that matched the onesie. Me and my fiancé decided we wanted to try for another baby because we want a baby VERY badly. And almost immediately again we got pregnant, we had promised each other we wouldn't get excited but yet again we did... we celebrated and everything and then all of a sudden I woke up one morning having pink spotting. I know not a problem probably implantation bleeding I thought. Until I started bleeding MUCH heavier and another miscarriage at 5 weeks. It's going on day 9 of me bleeding and all I have coming out is black blood and I'm in excruciating pain... I haven't really made a point about it to anyone really since I don't want to complain and seem like a baby but honestly I know it's not my fiancé who has the problem as I have no problem getting pregnant...i just can't keep the baby long enough to carry it to full term. It hurts knowing I'm the problem and that my body won't accept our babies....I just don't know what to do anymore as I can't even do the one thing I was made for... bearing children....