What Causes Irregularities In Periods?

hi am 34 years old. have had some terminations done for the past years. my recent terminationwas on 5th jan 2010. got my cycle on 26th feb. have not got my next till now .offlate my cycles are not regular. my weight is 70kg and ht 5.1ft. kindly let me know my problem and alsohow do i get rid of this. thank you