Last Week My Son Had Hives. Started In His Back

Last week my son had hives. Started in his back and worked it's way up to his head and down the front of his body. Took 3 days to clear up. He seemed ok but now a few days later, he is suffering from joint pain and says his neck hurts and he feels weak. No fever. Slept most of the day today. Yesterday he complained of a stomach ache and again today as well. Never seen him like this before.