Metformin has no effect whatsoever on Parkinson's disease, therefore stopping it wouldn't change the symptoms but rise your blood sugar levels unhealthily.
There ist no natural cure against Parkinson. But isn't chemistry nature, too? I would like to reassure you to take your medication again to improve your life and relationships.
This is a real bad story you tell hre! I am sorry about your mother. This won't happen to you if your GP takes care.
There are no dietary rules for Parkinson.
hre is more about diabetes: http://www.diabetes.org/food-and-fitness/food/planning-meals/.
All the best!