I Relapsed After Being Clean From Meth/ice For 90 Days

I relapsed after being clean from meth/ice for 90 days last week after using for 17 years and ever since I shot up I have a hive like rash behind my right ear that goes along my hair line all the way to the center of my neck and continues down the nape of my neck. It comes and goes throughout the day. Usually worse in the evening. They aren't meth sores and sometimes get swollen almost like swollen lymph nodes... Any thought on what it could be?