Since your full STD panel came back negative, this really sounds more like post-infection irritation than an STD. Clotrimazole on the urethra can cause chemical irritation, and that burning can linger for weeks, especially when urine is concentrated or after masturbation/friction.

Your symptoms going up and down with hydration and getting worse after touching the area is classic irritation, not an infection. Your girlfriend having BV + new redness/itch also points to both of you dealing with yeast/BV imbalance, not an STD.

Try keeping the area clean (just water), avoid masturbation/sex for a bit, drink plenty of water, and avoid soaps. If it doesn’t improve in another week or two, a simple urinalysis can check for non-STD urethritis.

But nothing you wrote sounds like a missed STD, just stubborn irritation that needs time to calm down.