What tests and stuff after many mc

Katie
I've have 5 losses. I would like to know what kind of tests or treatment is available to help determine y I'm loosing them, and how to keep it from happening. I know I'm o-, and have herd it causes issues. Could that be the problem?  But I need to know what's out there that can help Bc like everyone else on here, I want my little one so bad. Please help