implantation bleeding ?

okay so im 16 and i have this one sexual partner who is 18 and has about 30ish bodies... but we recently just hooked up again and its been about a week and i started bleeding out of nowhere, its not enough to be a period but its too heavy to just ignore i only see it when i pee and when I wipe. we used protection but could it be implantation bleeding or an std? I also had my period literally a week ago so it cant be my period since they are very regular.

i also just started a pill for a uti and i started taking it a day after my period ended so i was thinking maybe the medicine is letting the rest of my period blood out that couldn’t get out bc of my uti? i dont know i’m just concerned.

my mom has agreed to get me tested for stds but I am still wondering if it could be implantation.