HELP!!!

I’m having constant irritation on the skin right outside of my vagina. It’s red and itchy. I only use Honey Pot feminine wash, no powders or sprays, and Niacin cream that was prescribed. When I use the cream it goes away for a little bit but if I have sex it comes back. It’s not an STD as I’ve been tested every time except recently. I don’t know what to use to help get rid of it permanently so I don’t have to go to the doctor every month. PLEASE HELP! I have a picture but I don’t know if I can post it.