Sex positions

I'm 28 weeks pregnant. Me and boyfriend since we have been together which is over 2 ½ years we have only had sex in the missionary position. Which I dont mind because i can always orgasm in that position but I secretly went on his phone and saw the kind of porn he watches. He likes girls on top which I cant do as I have a tilted uterus so he cant get it on. I want to try doggy style but he said hes frighten he is not big enough to get it in. Just a heads up I am a big girl and he is a very thin chinese man. I just need some help. I only slept with 2 men and that includes my boyfriend so I'm very inexperience and he is the same. He slept with a prostitute when he is 18 and she basically just got on top of him and did all the work. He didn't see a vagina face to face until he met me. Like he had to figure out which is the right hole. That was the only girl he slept with that wasnt me. So he is super inexperience too

Just to add

This post is to basically ask for advice on how to initiate new positions

Also I've tried it on top when we first met and I couldn't do it. I couldn't do it with my first boyfriend either.

I just want some help on how to try new stuff