What caused my yeast infection? 🤔

A little over a year and a half ago I had my first (and so far my only) yeast infection. I was 17 at the time and i got it right after my first time receiving oral from a guy I was hooking up with at the time. BUT That happened right after my period ended and this particular cycle was my first time using tampons for the entire duration of my period (I had only used a tampon on one or two occasions before but not for long). So I told my mom that I was having some real bad itching and soreness down there and she concluded I had a yeast infection so I got some monistat, stayed home for a day, and everything was back to normal. I never told my mom I got oral (she’d freak lol) but I told her that I did use tampons for pretty much the first time the week before so she assumed that I got the infection because of using tampons, but I’m not sure if it was because of oral or the tampons.

This isn’t a pressing matter, but I’m still curious to this day what caused it. 🤷‍♀️ I didn’t change soaps or underwear or anything. I haven’t gotten one since, and I now use tampons regularly.