GF not satisfied

I (28M) and GF (25F) have been together for a little over 4 years. I have been in a few sexual relationships in the past so I had an idea that I was average in bed. In my previous relationship, I was able to satisfy my ex (made her finish) and it just helped me do it better. However, I am not able to satisfy my GF. She had never done it before I met her. I have tried a lot of things (mouth, hands, consistency, toys) but she either gets tired or it starts to pain her down there. I am having these thoughts lately if we are sexually incompatible. I have immense love and respect for my lady and really want to spend the rest of my life with her. But this thought of sexual incompatibility and not being able to satisfy my girl worries me. What do I do?

P.s she has never experienced an orgasm before.