Hi R, You may find that this is vaginal spasms, there is a band inside her vagina, and its this that can go into spasms, and when that happens it gets tighter, may be from having a girls time.
Do hope this helps.
Good Luck
She is self-lubricating well, and we always use foreplay. It's not a big problem, it's just that her vagina is much tighter than it was 5 days ago and I'm curious as to why. Everything is as it should be, except for the extra tightness and it hurting a little when I enter her. Once I'm inside, there is no more pain. It's just at the point of entry, she feels like the opening is being stretched. I guess I'll see where things go and update as best I can.
Probably her mind is not on sex.or not excited sexually.Foreplay may help. Lubrication can also help to have painless sex.