What Causes Irregularity In Periods After Being On Nicotine Patches?

Hi i have been on the nicotine patches for 3 weeks and on the pill for 4 weeks and I am a little concerned as I have had a period on the 29th December which lasted longer than usual and have started a period again on the 18th January which is rather unusual as I am a 28 day cycle. Do I have anything to be concerned about?