It doesn't sound like you "thinned the skin," even if your skin had a reaction.
The skin is a regenerating organ, and even if you did something (like for example scrape or burn it) it would heal and look normal quite soon. It's hard to understand where you get the idea that what you did for such a short time with that product would "thin" your vaginal skin.
I don't think this will be a long-term problem, semen has steroids in it too, and the vagina is built to take semen without problems. Talk to your new doctor and see what he or she says.
Sorry, that first sentence was supposed to begin "I wish you would not just doctor-shop"
In other words, I hope you will try to find it in your heart to believe the doctor.