Inka, you need to get help immediately if you are worried about taking an overdose. I would suggest calling the people who are already familiar with you, but you seem not to trust them. So, why not call your local suicide/crisis hotline? Or just go straight to the emergency room.

You need to get immediate help, especially if you suspect your doctor and case manager of trying to poison you. They probably just want to help, but perhaps you would be more willing to accept help from someone else.