Hi. It's not for me to diagnose you, but if the docs say it was too early for gestational diabetes then it implies that it could be Late Onset Type 1 (LADA) which is effectively what the docs are saying. This is usually the result of antibody attack on the pancreas and tends to occur before the age of 30'ish and you would not normally be overweight. There is a test called GAD which may prove the presence of specific anti-bodies but there are others that may not show up. The treatment would be insulin if tablets fail to work initially or the blood sugar has already progressed too far. So, you are unlucky but this can happen to anyone even without any family history.