Infertility reasons

Hi,

I’ve had 2 failed rounds of clomid, currently on 3rd. My partners sperm was fine last time we checked. Haven’t had a recent scan but 4 years ago it was fine. I am ovulating, confirmed with follicle scan/blood test, so the dose is not being changed. I’m feeling like there could be another issue. Do you know what else could be causing infertility? I do have a son and I had a late miscarriage 2 years ago now. It’s heartbreaking I can’t get pregnant. I just don’t understand why.