Hi, I Have Been Taking A Oral Birth Control For

Hi, I have been taking a oral birth control for about 4 months now. I take it religiously, within 20 minutes of the right time every night. I have 3 active pills left, my period has been beginning 2 to 3 days after my active pills end. Tonight, I went to the bathroom and wiped and there was brown blood which has lightly continued.
I am sexually active without a condom, we combine the pull out method with my birth control pill.
I have also read that having diarrhea can cause break through bleeding, but I take my pill at 8:30 PM and had the diarrhea at 11 AM. Unsure if this matters at all.
Please help me get to the bottom of this! Thank you so much.