What causes swelling allover after I itch the spot and after it goes away I itch another spot and irksomeness again?

Dermatographia. Surely sounds like urticaria or hives - most likely dermatographism.
Probably histamine. If I understand you correctly, your skin gets itchy and after you scratch an area it swells up right where you scratched. The swelling goes away. But the same thing happens when another area gets itchy and scratched? This sounds like a form of hives called "dermatographism". It is usually not serious - mostly an annoyance. You can take an otc antihistamine daily for a while and see your dr.