What Causes Red Bumps All Over The Body?

Hi. My brother he is 11. and he has these huge big and small red bumps all over his body. Its his arms, back, stomach, and neck. They get flary/irritated when his body gets warm or hot when he plays. and there just gross to me because there red huge bumps and some are connected together within his skin. They tend to itch him sometimes. We give him anti itch cream and A special lotion We ve taken him to the doctor twice to get 2nd opinions. And they both said it was a virus going around but he s had these on his body for about a month or so. 2nd doctor gave him pills but its not doing a good job its been a week he s been taking them. So do you have any idea of what these bumps could be? Or what treatment options could be?