Sore Vaginal Opening

Hi so this post is gonna be a little TMI, but I don’t really know where else to go. So to start: my boyfriend is in the military. We go at least weeks at a time without having sex (he’s not stationed too far so we always make things work and see each other often). Whenever we do get to see each other, of course we do the do. My problem is my vagina gets easily sore, and I’m not sure why. Like I have to be careful with how often we have sex because say we go 3 times in 2 days: I may not be able to have sex for like the next 2 days because because my entrance hurts. I will even be a little tender when we go to have sex if we’ve done it once before. Anyone have any idea on why this could be? It’s really frustrating to me, and I want to get to the bottom of it. Any advice is GREATLY appreciated lol i’m about at my whits end with how fragile “she” is.

Edit: thanks guys! I thought I was plenty wet before, but these comments have made me realize that adding in lube can only do good lol