Vaginitis or?

Okay so October 17 of this year I went to the ER because of vaginal rash that was itching so bad and I had no discharge. This comes after a week of having sex with a new partner. There were a few bumps around my vaginal area so I immediately assumed std but of course I didn’t assume I got it from this new partner cause I know it takes a few months for you to get a reaction or symptoms so I thought it was from my kids father but was also unsure because him and I lost our Virginity to each other and neither of us slept with anyone else until after we ended our relationship for good a year ago. I never got a rash like this or any itch or bumps my whole life especially while being sexually active. Never had a yeast infection or anything. So at the ER I explained to the dr my symptoms and told them I wanted to be tested for any and every std cause that’s my biggest fear. The physician looked at vagina and said it doesn’t look like genital herpes so he didn’t test me for that but he assumed it could be Chlamydia. I got tested for that and gonorrhea and some other stds. He prescribed me doxycycline which I take 2 pills for 7 days.

Results came back like a day later and I was negative for every std test done but also I have acute vaginitis and acute cervicitis.

Fast forward it went away after taking the prescription.

So today I’m having the same symptoms again but this time like yellowish green mucus discharge but no bumps just a rash and a itch and a few days ago I had sex with the same partner. I know for a fact he’s not sleeping with other girls but I’m just confused to why I’m only getting this now after having sex with a new partner who’s not sleeping around. Like I take care of my hygiene really good and he always showers before we have sex so can someone give me some kind of clue why it could be happening every time or has experienced this.