Will Immunization Shots Cause Skin Allergy?

My one year old just had immunization shots about a month ago and just started getting bumps on his elbows. Then I started to see them on his knees and now they are all over his body. They don t bother him and some are red but some are skin just skin color. Went to his dr yesterday and they said to use cortizone and benadryl. They are still getting worse and I am worried. Any ideas??