I Am A 38 Yr Old Woman. Generally Healthy. Not

I am a 38 yr old woman. Generally healthy. Not on any medications. Take a multivitamin, but not daily and haven't for several days. I started having a rash yesterday with no apparent trigger. The rash is hot and red and itchy and at times has hives. It doesn't stay localized, moving everywhere my clothes are constricting. I also had half of my tongue swell last night but no shortness of breath. Today I also noticed a deep pain between my shoulder blades which remained for approximately 10 minutes. It did not radiate, and I had no sweating or shortness of breath. I am only taking Benadryl to try and control my symptoms. When should I see a doctor?