HELP! I need sex position Ideas

[MrPinkTip]

I have a gf who is no fat but has a big round ass. I am having trouble finding positions where we can fuck. My cock length is about 7inches and I have never had this problem before. When I try to fuck her doggy I can't get that deep or pull out that far. The only positions we do regularly are missionary and her on top. I need some suggestions?