Hi, While using oral contraceptive pills sometimes menstrual irregularities can be seen as side effects. They can present with inter-menstrual spotting, breakthrough bleeding, hypomenorrhea or amenorrhea, etc. Though you had moderate flow in previous cycles, this irregularity can develop after a few months of usage of pills also. So, possibly the brown spotting you had at the time of expected periods can be considered as your withdrawal bleeding only. If you have not missed any pill or not altered the time of intake of the pill, the possibility of pregnancy is very less. Taking the pills, according to the schedule irrespective of the menstrual flow will maintain the contraceptive effect, so you can continue with your schedule. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sree Gouri S. R., OBGYN