What Causes Irregular Periods After Taking Tablets To Postpone Periods?

hi am 24 years old.my periods was regular and its 28 days cycle.but after marriage ( 1 and half year 2 times i used tablets for postpone periods for my broth marr and for my marr) but from past 3-4 months my cycle was disturbed. 25 day s and now 33 to 36 days...am not understanding why my cycle was changed.