cici,first of all dont worry,there is nothing wrong with you,if you miss a period,it happens with most women atleast once or twice in their life. reading your history and as far from my experience in similar cases,metformin can be one cause,especially since you had regular periods before. antidiabetic metformin causes hormonal changes in women and also impact their regular menstrual cycle. The drug works by stopping insulin from affecting the hormonal function. Therefore, women who take metformin may experience no periods, or infrequent or delayed periods while taking the medication and i assure you are not alone. i would advise you to stop metformin for a month or two and you will probably see you periods back to normal.And for the weight loss,instead of metformin,pls have a good diet and do have an exercise regimen involving aerobic exercises and mild weight training. Hope i could be of help.