Scanty Period

Hi, i’m 19 and my current “period” is extremely light and diluted. Usually, i have a super heavy flow for about 5 days straight. This app is usually accurate for me and the spotting started the day my period was supposed to start but i continued to have spotting the next couple of days and only when i wipe usually (my urine is normal colored though). The last time i had sex was probably 2-3 weeks ago but a condom was used and he didn’t finish in me. I also currently have a uti but online it says uti’s don’t usually affect menstrual cycles. I have no idea why this is happening and really hope it’s not something serious, especially not implantation bleeding. Anyone have any advice or similar experiences??