3rd miscarriage

So I’m currently going through my 3rd miscarriage.

I have no children of my own. First miscarriage was May 2019 around 9w3d, I watched the heartbeat stop during my ultrasound. Second was August 2019 7w1d, no real reason. Third 5w3d, HCG slow to rise Progesterone stayed low at 8.8. I didn’t even tell my husband this time because honestly what’s the point if I’m just going to lose it anyways?

I’m 27 and healthy, my husband has a daughter from a previous relationship.

Why can’t I just carry a baby? I work at a hospital where I see people come in all the time overdosed on meth and heroin that find out they are pregnant and the carry it to term while still doing drugs. But me? I drink tons of water eat pretty dang well, and am decently active, yet I can’t even get passed 12 weeks.