Help please

My husband and I have been struggling for almost 2 years now. Last December our first <a href="https://glowing.com/glow-fertility-program">iui</a> worked but ended in a miscarriage at 12 weeks (8 weeks gestational) in February. We then got pregnant with our 4th <a href="https://glowing.com/glow-fertility-program">IUI</a> last month (June) but that ended in a chemical. My HCG only got to 8. Now this month we got pregnant again with an <a href="https://glowing.com/glow-fertility-program">IUI</a>, but my HCG was only a 24 at 14dpiui and I'm pretty sure it's going to end in a chemical too. Does anyone know what could be going on? Why does this keep happening? Is it just bad luck or could something be wrong? All my tests came back normal. I'm on a baby aspirin and progesterone. I'm just about to lose my mind and don't know what to do. Why does this keep happening?