What Causes Inflammation And Itchy Rash On The Back?

I was operated about a pilonidal sinus 4 months ago and was taking Metamizole (dipyrone) and Paracetamol (acetaminophen) every 6 hours for pain. After 2 weeks I noticed an itchy rash on my back. I also noticed inflammation after I scratched any part of my body. The nurse said it was due to an allergy to the medication. After a few weeks the rash disappeared but inflammation still happens when I scratch any part of my body. (Especially if I scratch my face which becomes very inflamed and it looks as if I was deformed.) This inflammation takes about 10 minutes to appear after I scratch and lasts about 1 hour. What can I do so that inflammation stops occurring ?