Rashes and blisters on skin with itching

My mother has been suffering from red rashes all over her body except hands and legs including breast,neck ,back and abdomen first i started on breast and abdomen with small bumps and later it has spread to neck and back since she has scratched it because of itching and it didnt spread to any family members .The rash was associated with small and large bumps with severe itching .recently she has diagnosed with diabetes and taking metformin at morning time .blood sugar levels and hba1c levels are under control.we have visited general physician for the skin rashes and the doctor has prescribed Levocitrize and told its bacterial infection and treated with antibiotics injections .The flare ups got reduced sonewhat but again it has spreaded and started severly we consulted dermatologist he told its viral infection and takes time to reduce it and prescribed levocetrizine again with topical cream of betamethasone dipropionate cream at night .it didnt reduce it .what is the exact diagnosis ?