Hi and welcome to the site. My name isXXXXX hope I'm able to provide some helpful medical information for you today.
On low dose BCPs, the bleeding pattern can shift slightly sometimes. This is usually not anything worrisome. Brownish color is just old blood that was left behind and didn't get shed during the normal withdrawal bleed time. For now it's perfectly safe to keep an eye on it. First check for a retained tampon. But if that's not the case, watch it as long as there isn't any odor, burning, irritation, heavy bleeding or anything else concerning. As long as it's just dark spotting and you otherwise feel well, it's fine to watch for one cycle. Doing a home urine pregnancy test would be a good precaution to take too although risk of pregnancy is quite low.
The last time I had sex was May 24th, when can I take the home pregnancy test?