I know you don't want to hear it but from going they gd myself and all the educating and research I did it sounds like you just have no control over this by diet control ;(
Your body is going to need insulin and then you can go back to eating those healthy foods that will keep the weight on. It sucks I know but it doesn't mean you need to be induced if you can preempt it start doing those 'tricks' towards the end if your pregnancy to help labour start on its own