What does a fertility specialist do for recurrent miscarriage ?

I’ve had 4 miscarriages now and my doctor did all the tests he could and has found nothing wrong me. I was even on progesterone with my 4th pregnancy and it still ended in a miscarriage. I’ve done 2 rounds of clomid and got pregnant from 1 of those and still miscarried. I’m not sure why everyone tells me to see a specialist because I had a consult with one and she said they do 6 rounds of clomid and if nothing move onto IVF. I cannot afford IVF. How can a doctor help me stay pregnant ?? I feel like it’s over for me