So confused!!

So we've had 3 miscarriages this year (one at 12 weeks in February, one at 4 weeks in June and one at 6 weeks in July). My infertility doctor decided it was time to run tests to make sure everything was normal. Well it is. All the blood clotting tests and chromosome test came back normal. So what the heck is going on?? We are already at an infertility doctor and have <a href="https://glowing.com/glow-fertility-program">IUI</a>'s each time because I don't ovulate on my own. So are we really just having bad luck each time? Has anyone been through this? What happened? Thanks for any advice!