std, yeast infection, what could this be?

i (F18) am only sexually active with one person, and we’re each others only. and i noticed my vagina starts burning during sex and afterwards the inside feels irritated and itchy. it used to kind of hurt to pee, but when given lots of friction. at one point it went days with the inside of my vagina feeling like rug burn. when the symptoms subside, and we have sex again the symptoms come back. i noticed a thick cottage-cheese like discharge, even after taking a 3-day yeast infection treatment. i’m almost convinced this is some type of infection because i never had issues until now. what do i do? and what could this be? the inside of my vagina feels irritated.