What Causes Fatigue And Brown Rash On Back When Suffering From Erythema Nodosum?

A year ago, I was diagnosed with erythema nodosum. I am feeling fatigued and run down again, and although I don't have the painful nodules on my legs, I am achy and I have developed a light brown rash or spot on my lower back that looks almost like a burn scar. Suggestions? I am 15, 5' 6", 120 lbs. My brother has chrohn's disease, so possibly other autoimmune disorders run in our family?