What Causes Light Period And Weight Gain?

hi iam 25 yrs old ' a yr back i have regular periods for maximum last 4 days, but now iam having mi periods finished in 2 days with a very low bleeding, i have put on weight too , and mi bra size has also changed , few weeks i consult a doctor and she she told me to take a daily bases walk or a routine exercise, and a medicine called glucophage nand some dioet to follow, i want your opinion on that .. thanks n regards: maya