This is going to sound weird and perhaps offensive as well but I do not mean it in a negative or rude way.

My(23) girlfriends(25) vagina essentially though is like a cave, when we have sex she is super awkward about it and I never finish. It's like the entrance is tight but after the intrance it's like the walls of her vagina just disappear literally feels like this sort of shape () when typically with women In the past theirs has been more like )(

I have not finished a single time from vaginally sex with her like I normally would with other women but not going to break up with her over something like that, that's ♥♥♥♥♥♥ up. I just need someone to explain to me why this happens and if there is a remedy?