What Causes Irregular Periods?

hi,last few months i have taken i pill,average 2 in a month and my period is totally irregular as it is coming every month 2 times,some times spotting,sometime lite bleeding,,not heavy bleeding.i am very tensed and decided not to hv i pill anymore.but at this situation is it bcz of i pill i m getting irregular period?plz advice.i m really in tension.i was never having irregular bleeding problem before.it started after taking so many i pill in last 3/4 months..