What Causes Skin Rash Under My Skin?

i developed a skin rash or humps for the past 6 monthsunder my skin on my back, heaps and breasts. it itches and pains at the same time- sometimes i get them under my feet and the inside of my hands and my fingers swells. My gp already gave me cortezone injections and pills, antihestamine pills, ointments ext, but nothing seems to work. he told me that it could be an allergy caused by food, something in the air that i breath in or the medication i'm using at the moment ( serdep 50 and jaz ). i did blood tests and don't have any allergy for any foods. please help!
please excuse my english for i am afrikaans speaking.