Suggest Treatment For Irregular Periods

My age is 22,i have irregular periods from the day when i become matured..its nearly 10 years..periods is coming only for every 3 - 4 months..i consulted four to five doctors..they told me take scan...but as by the scan result doctors are saying i dont have any problem..they gave 21 days tablet..i eat that capsules for more than 4 years..but till now my periods problem was not...Give some suggestion to cure it...