What Does Dark Vaginal Discharge When On Birth Control Pills Indicate?

Hi. I recentry started birth control and had unprotected sex about a week ago. But recently my vagina has been smelling different and a bit off. I know it has a certain smell and thus is not one of them. I have discharge but it s not thick or gooie or really anything you can see. I had some dark fluid come out which I assume is just old blood and spotting from my last period. But the fluid/ discharge I guess is clear and just makes my underwear wet. I guess it smells fishy but it also smells like a little but of poop. I m not sure what it is Going on. I know that birth control may change some things but still.