UTI questions

Hey! So it’s my first ever time getting a uti, so I have some questions about them. I am currently taking Trimethoprim and drinking A LOT of water, I’m almost on the start of day 4 of it. I haven’t noticed any change with anything, it still burns to pee and all that. How long does it take for the medication to feel like it is actually working? Another question I have is, is it normal for my inner labia/vaginal opening area to have reddish marks on it, and some white-ish marks on it? I’m assuming that is just from irritation. Also, my period happened to come during this uti period. Is that going to make my uti worse? Thank you in advance, I almost made it two whole decades without getting a uti 🥲