Advice needed on how to control my unhealthy diet

My relationship with food has always been terrible, even before I was diagnosed with autism.

I would eat very large plates of food as a child, and would pick off of other people's plates once they had finished. I loved sweets, so much so that when my mother started to hide the sweets, i would dig through the cupboards until i found them. I ate and drank things so fast that i would have frequent nausea. I never stopped mouthing, so any pen, pencil, lid or bottle cap would either be chewed to an unrecognisable clump of plastic or swallowed.

Even with the diagnosis, i haven't seemed to control myself. I know now that i mostly overeat because of a lack of mental stimulation and because of sensory input, but I can't change my diet no matter how hard I try.

However, i do worry that at the rate i am going, i could end up with diabetes. 

Any advice would be greatly appreciated.