Turns out it was simply because I'd missed a day and had to double up on pills. It stopped the next morning.
Hello,
It could also mean that for whatever reason during your last menses the entire uterine lining failed to make a timely exit. In some cases however there is cause for concern like cervical cancer, pelvic Inflammatory Disease (PID), menopause, or sexually transmitted diseases like gonorrhea and Chlamydia .You should consult a gynecologist for evaluation.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.