It has nothing to do with what you eat, how much you eat, or weight. Sometimes the body can't handle the increased stress on the pancreas due to pregnancy, as a result GD develops.
It's all to do with the placenta causing insulin resistance. It's nothing you did or didn't do. There is a good thread on it on the high risk board. Personally I'm sending you a giant hug, you can do it! I've been on the GD diet since the end of March, it's hard at first but you'll do great!
You should know it has little to nothing to do with diet. Didn't you say your doctor is sending you to an informational class in your other post about this in the N15 group? The class will help you understand this condition better than anyone here can.
Re: 30 weeks pregnant and 1day I have gestinal diabetes