Having trouble doggy & riding.

Hi everyone I am not new to sex I’ve had multiple partners that I was able to do doggy with and was easy to ride. I have a new partner and he is new to sex he doesn’t have much experience but we cannot seem to do doggy style or have me ride him without the dick slipping out/ having trouble with the rhythm, he asks me if I just don’t know how to ride dick or doggy but I’ve done it multiple times in the past I’m not sure what’s the problem. I feel like I’m starting to think maybe I don’t know how to do it but I know I’ve done it in the past it’s making me kinda self conscious any tips/ ideas? :/ all we seem to get down is missionary but I’m tired of doing the same thing every time I just wanna do different positions 🤦🏻‍♀️ but I feel like I may be the problem