Why My Doctor Has Prescribed Me Metformin?

i am taking yamini from last 3 years . i had irregular periods before marriage. with yamini i am taking metformin SR 500 mg . my insulin levels were absolutely normal before i started taking metformin. but abruptly increased to boundray level when i stopped this tablet in between prescription for 2 months.
i just want to know that is there any means to get rid of these medicines?? i am 25 yr old my weight is 64 kgs with 5'1" height. i just want to know that why my doctor has prescribed me metformin??