I Have Started To Develop An Allergy,it Appears As A

I have started to develop an allergy,it appears as a small pimple and within minutes its grows bigger and extends to other parts of the body,its red in colour and I would rely on allergex each time they appear,my doctor has given me injections on my left arm and they would go away and come back maybe after two weeks ,he advised me to just ignore when it appears and should not scratch as it will go away in no time,and yes when I ignore it just appears and go,please help as I can't rely on allergy pills and don't want it in my body,worried.