Have skin problems been ruled out? I didn't have the same symptoms as you, but I had severe itching on my vulva as well as soreness and sometimes some of the skin starting to split. The friction from sex and my vulva being touched a lot made it worse at times. I was concerned about STIs but all my tests were negative, so I went to a private dermatologist who has particular experience with genital dermatology and was diagnosed with genital psoriasis. Steroid cream and emollient has helped quite a lot. Not sure if this is relevant to what you're experiencing, but thought I'd share just in case it might be of any help. Hope you get some relief soon!