Hey fellas, wanted to know your opinion on this:

I'm a 22yo, been dating a 22yo religious girl for 2 and half years. I was my gf's first sex partner, and even though sex is really good and has always been practically on demand (I can think of a couple Hard No's in during the relationship), we only do it missionary or With her on top, and i can't get her to do some fun positions like doggy/anything from behind. From the way she reacts i think it makes her feel slutty and she feels she wont be able to enjoy. Sometimes With clothes on i'll bend her over and grope her breasts and i can feel she becomes really horny quickly in that position, so i can tell she likes it, but so far no success in the sex department With it.

Any advice i can use to turn this around?

I'd be glad to give out more info if you find it necessary to get a clearer picture. Thank you all for your time, in advance.