I too have dealt with this! Our bodies are so peculiar every given day of the week. I found that if it’s my first time having sex in a few days, I’ll pick a position where I’m in control, usually me on top of my husband. Since it’s my first day in quite a few, I expect I’d be sore afterwards.. but using lots of lube and not going really rough(after a break from penetration, I tend to be tighter) usually helps me!
If I have sex the next day too, I know my body will be better prepared and we can go more rough.
You have accomplished so much and everything seems like it’s going really well! I think you may just need to tune into yourself and see what may be causing this.
Have you thought about a semen allergy maybe? I know a lot of females get really sore 5-10 minutes after having semen in there.
I hope this helps!! Oh, you can also use a nice warm cloth or even a cool one down there, it really takes the swelling and soreness out!