My 4 year old daschund has been having severe itching all over her body.?

There are small eruptions all over her body along with some areas of loss of fur at some places. There are also marks or calluses at the joints of her legs which also seem to itch a lot. She gets temporary relief from antihistamines but the present treatment she is getting from the vets including therapy for fungal infection and filariasis do not seem to be helping much. Does anyone have any suggestions to solve her problems? We stay in Kerala, India -- where the weather is sultry the year round