I had gestational diabetes and afterwards my fasting sugars in the morning were right around 100. is that enough to put me on metformin ?

Possibly : This depends on your physician. If you have impaired fasting glucose, your hba1c may be abnormal and should be checked. You may also be asked to check some fasting and 2-hr post prandial glucoses before medication is considered.

Depends-Yes: Studies show that most women with gestational diabetes that are not properly educated/managed become diabetics in ~5-10 years. Depending on your family history, medical conditions, body weight etc drug therapy/ life style modifications may delay/prevent the onset of diabetes. Metformin alone has shown ~ 35 % reduction in diabetes in obese patients. Diet/exercise plus metformin works better.