Why can’t my body sustain a pregnancy?

I’ve had 3 chemical pregnancies with no full term pregnancies and we don’t know why yet. I’ve had an HSG which showed my left tube is clear but my right tube might have a blockage/polyp/fibroid at the beginning of it. So my RE wants me to have a saline sonohysterogram tomorrow to take a better look inside my uterus. Do you think a fibroid or polyp could inhibit an embryo from implanting and cause a chemical? So much that it would happen 3 times? Would this mean I only ovulated on the right side?I’m just trying to understand why..😭