How can I treat my son eczema its all over his body and its swoll he can sleep?

Here are some tips. Eczema can't be cured but usually can be controlled. It's best managed by using a sensitive skin cleanser, avoiding bathing in very hot water and bathing him only every 2-3 days, and using a sensitive skin lotion at least 3 times daily, even when the rash isn't there. Ask his doctor if you can give him Benadryl (diphenhydramine) before bed. If doing all this doesn't help enough, his doctor can add eczema ointments.
Eczema. You are describing severe eczema that is so itchy and uncomfortable it interferes with sleep. It is best to see a dermatologist. Often fragrance free moisturizers and topical corticosteroid or non steroid creams, and antihistamines are prescribed to control the itch. In some cases, bacterial infections may result if the scratching creates open wounds.