What Causes Large Red Patches On Legs And Torso After Taking Metformin?

My Dr. Put me on metformin for 1st stage diabetes2. I broke out in large red patches on my legs and torso. Dermatologist put me on prednisone 60mg per day for 4 days then 40 tapering to 10 to none. All was well. I was told allergic action to metformin. Dr. Put me on glimeride. Same thing only prednisone does not do anything now. My BP is now running 160/71 and blood glucose is around 160. I have been taking lisinopril for BP and atorvostatin for cholesterol for years without incident. I am not on any mess now trying to figure out what is causing rash and blisters. 65yo male 6'1" 210lbs would an antibiotic be in order