Septate or bicornuate uterus? Doctor doesn’t know

Ok ladies. I’m at my breaking point with confusion. So I’ll start from the beginning.

I got pregnant with my son on the first try. Super easy and uneventful pregnancy. Aside from a long labor, I gave birth to a 9lb 10oz 22in baby vaginally who came at 41 weeks. Never had any issues afterwards.

I got pregnant again which was a surprise. But we were excited. Unfortunately I had a miscarriage which resulted in a d&c. And that’s when the problems started.

My first two cycles seemed normal (6 days long but heavy to moderate to light to brown spotting). Then I had a lighter period(still 6 days) on the third cycle. Got concerned and told the doctor that I was concerned about possible scarring. She said it was rare and checked if I was ovulating. My progesterone level was 27 on day 8.

So then I had cycle 4. Another light period. So I saw another OB. Told her I was concerned about scarring. She assured me that was rare but ordered an hsg. And wanted me to come in for a pelvic ultrasound. Go in for US and thought she saw a possible sub-septate uterus or maybe bicornate.

Then cycle 5 and another lighter than my normal period. Hsg comes. My left tube was blocked and the radiologist said that was most likely scar tissue. But my OB, She still couldn’t tell if it’s a septum or bicornuate. Just told me that the right horn was open and clear and the left side had a small horn. So she ordered an mri and referred me to the fertility clinic.

I am so confused. Everything I’ve read about septate and bicornate seems like I wouldnt be able to give birth vaginally since they run out of room to grow? Normally have early births also.

My husband is convinced that it’s scarring from the d&c pulling that left side of my uterus down. And honestly I feel like this as well due to the lighter periods. It’s still the same length of days. But the bleeding is just not like normal. Might have one heavy day and the rest are light or brown spotting.

How common are bicornuate uteruses? Is it common to not see them on ultrasounds??