3 miscarrieges and not able to stay pregnant

I will explaine my situation. Hopefully somebody is in the same position as me.

I already have had 3 miscarrieges and I never van stay pregnant. My body is not Able to keep it alive. Never came by the 12 weeks. There where tests done on the baby last loss and There was nothing wrong With it. It was fully healthy but it still not survived. 3 times off ‘bad luck ‘ I don’t believe anymore. Doctors don’t want to investigate why it keeps happening. So I have given up on my chance of a family of my own. And will start taking birth control to prevent more Losses of babies. Because I can not take anymore losses.