What Causes Irregular And Abnormal Periods After Missing Birth Control Pills?

hello. im currently taking syronx for my brithcontrol. i missed 2 days the 7th and 8thday pills. i doubled up the following 2 daysjust like it said. i began to spot on the 10thday of the pills(tuesday) and cramp. i ve had breast tendernesson and off throughout the month. i spotted/bled for13 days! this is very unnormal for me im very regular usually only 3-5 days max. i took pegotest multiple all coming up neg. on the 2ndday of the placebo it stopped. i went to the doc the 2nd day of placebo and she gave me a prego testand checked me out and everything was ok. i had papsmear and stdt testing last month and all was good. she told me i should have my normalperiod again anyday but yet to see it. ive beenon bcon and off for 8 yrs have misseddays and never had this happen before. concerned.