Hi. I cannot say for sure, but you might have him checked for allergies. I have seen kids who had allergies act this way when exposed to something say a cleaner or perfume--a chemical allergy.
Beyond that, have you tried setting a few min. every day for just you and the child? Middle kids can feel ignored, even if you try to be inclusive. Give them a few min., read them a story or do some coloring together or hold them while you watch their fav movie. It might work.