I Am Taking Care Of My Mom's 12 Yr. Old

I am taking care of my mom's 12 yr. old diabetic poodle, The peron who took care of him prior to me, overdosed him on insulin. He was at ER vet 5 days. I understand diabetic dogs are thirsty. This poor little guy is so insanely thirsty. Constant piddle puddles even without water for a couple of hours, and is looking for food as though he is starving. He is having excessive BM's, they are firm, but constant. I am afrid his sugar is out of control, or maybe worse. Any thoughts of wisdom for me...please.
Thank you, Cynthia