6 Year Old Having Skin Rashes On Arms, Legs, Face And Chest. Appear In Clusters. Could It Be Due To Gluten Sensitivity, Impetigo Or Poison Ivy?

My six yr old has a rash tha,,t is random in no pattern on his legs mostly then arms and the least on his face neck belly and chest.It s clustered in areasd in other areas they are singular.His knees have the most bumps and the most clusters.They are are slightly raised and some are pink while others remain his normal skin tone. They have small roundish blisters. They re itchy and spreading I believe. The ones he has scratched open become scabbed and appear to have a dot and resemble mosquit bites ..Based on my research it sounds and looks like possibly impetigo , poison oak sumac or ivy, hives (he has had them previously ),a reaction to a gluten sensitivity or a flare up of the coldsore virus which he had a very serious case of as a toddler that affected his entire mouth inside n out and all around his mouth There are 2 adults and an 18 mos old also in the house with direct skin to skin contact with him daily and none of us have caught it.He s had them over a week. Please help :(