This discharge came out and doesn’t make sense

So I’m on the pill (sprintec) and I’ve used it continuously, skipping the sugar pills to stop my period. My gyno recommended it, since I have a potential case for endometriosis, but I’ve been feeling fine, so there hasn’t really been an update on that, except my taking the pills.

This is the first time what looks like blood came out. My boyfriend and I do have unprotected sex, are monogamous, and have both been tested.

Has this happened to anyone else? Is it normal?