What Causes Rashes In Children With Runny Nose?

my 2 year old has had a rash on the right side of her body for a couple weeks now, I haven't been too concerned or taken her to the doc because it doesn't seem to bother her at all and she has no other symptoms, except for a runny nose on and off. But it's kinda weird that it is only on the right side of her body and has been there going on 3 weeks. Any ideas of what may be causing this and should i be concerned?