What Causes Mood Swings And Aggressive Behaviour In A Child?

I am trying to determine what might be causing episodes that my 5 year old son has. It has been going on since he is 2. He has poor executive function, has mood swings, can get violent, sometimes they are accompanied by full body eczema type rash, he seems to not make as much sense like speaking gibberish and mixing up mommy and daddy . It happens in cycles. He can have high fevers for no apparent reason. Had 4 high fevers this year, one with a slapped face rash. The last bloodwork showed low WBC and low neutrophils. Also he is super thin (eats well) and has low tone (getting worse) and poor coordination. We have ruled out celiac, thyroid, lyme, and food allergies. Would go with ADHD but the physical symptoms like the progressive low tone have us worried.