What has gone wrong in out relationship?

Good to see a serious looking question (in this subject). The best advice I can give you dude is to just be completely open with her about this subject. Confront her about it in concerned manner. Let her know that you enjoy being intimate with her and that when she turns you down like she has been, it takes a toll on your confidence. Things regarding this subject are best dealt with by being completely open with each other. Hopefully this helps and you two get back to where you were. Best of luck to you!