Mim,
If you have gd it means your body isn't processing sugars correctly and you have to watch your levels, initially by diet and exercise, then maybe by tablets and finally by insulin if necessary. Assuming your nhs trust is the same as mine you'll get a device which prices your finger and a wee machine which reads the blood levels from that.
My diabetic nurse said it's mostly a case of having a sensible balanced diet, watch out for low fat stuff as it's usually packed full of sugar instead.
I have to limit the amount of processed food, I've mostly cut out sweets, chocolate, fruit juice and high sugar fruit, i.e. grapes are dreadful.
I'm not too bad with carbs, but if you have wholemeal stuff that helps, think a gi diet kind of idea, things which are quick to digest and give you sugar spikes are bad, the aim is to have a lowish consistent level of blood sugars.
It isn't your fault though! Just one of those things that happens, especially if you were a reasonable weight to begin with!
You'll get more scans so you get some extra peaks at baby and you are likely to not go to your due date.
Hope this helps? Let me know if you want to know more?