Breakthrough bleeding???

Hi! So I’ve been on the pill for almost 2 years, I take it religiously. About 5 months into it I had weird stuff do they upped my hormone levels. I’m supposed to get my period on Saturday, but for the last few weeks (maybe like 2) I’ve been having brown bloody discharge. I’ve looked it up online and webmd says I’m dying but I know I’m not. I haven’t been having any other period or PMS symptoms. I started taking Zoloft in March but didn’t see any side effects regarding my issue. I started running 2-4 miles a day at the beginning of the month so maybe that?

Any suggestions or advice would be helpful