Gestational diabetes would not affect milk production. Feed often and frequently so that the Stimulation is adequate.

feed baby as much as you can... stimulation works best then try supplements like lactonic granules with milk, have lots of fluids...feed your baby alone with some music on....give skin to skin...if you are happy and relaxed your milk would increase no matter what...eat healthy... masoor Dal, green vegetables, ajwain and saunf boiled water also helps