I had gestational diabetes with both of my children.
With my son, it was easily controlled with diet. I highly recommend the Better Homes and Gardens Diabetic Cookbook - lots of great recipes and tips in there! I kept a log of everything I ate, saw a dietitian who helped me with adjusting the diet to find a good balance. It went very well and my baby was perfectly sized and healthy.
With my daughter, I had a worse scenario and needed insulin. I am terrified of needles, but I did manage to give myself the tiny little shots as I needed to. I was also managing my diet again and had more complications - my blood pressure shot up near the end of the pregnancy, so they labeled me "high risk" and I had a lot more ultrasounds. I am still battling the high blood pressure, but again - the diabetes went away immediately after she was born and I was able to resume a normal diet and stop taking insulin. She was also born perfectly healthy and not at all a "big baby" like everyone talks about.
Please know that it is not as terrible of a thing as it might feel. It happens to a lot of people and not on every pregnancy. As long as you listed to the doctors about sticking to a healthy diet (and take the insulin if you need it) you should be able to have a healthy, happy baby! Some doctors/nurses will seem overbearing at times, but just relax into it and stick to the plan that you and they put together. I know I stressed out every so often when one nurse I had would seem hard on me if my glucose numbers had gone up due to a family gathering or some other occasional food that I ate that raised it. But when the majority of my numbers were looking good my dietitian and doctor were very encouraging.
You will be at a higher risk for diabetes later in life too. I have recently joined a health club and have continued to use some of the recipes from that cook book in order to make sure I can be healthy and avoid it later on.
Good Luck!