Mysterious Red/Swollen/Hot Patch on Toddler's Leg

Let me first start off by saying I've already taken my (2.5 M) toddler to the pediatrician, and am waiting on a second opinion. The first pediatrician couldn't give me any type of a guess, but is running blood work.

My little boy consistently gets this red/raised/swollen patch of skin that is hot to the touch on the same leg, in the same spot, in the general same shape whenever he runs around outside in the hot weather. He claims it doesn't itch or hurt him, and benadryl/hydrocortisone cream doesn't help it go away. The patch only goes away with rest/cooler temperature.

I've taken note that no matter where we are outside (grass, pavement, rubber playground, woodchip playground, even sand at the beach) his leg will react, so it doesn't seem to be triggered by contact of allergens.

Has anyone experienced anything like this before?

Let me first start off by saying I've already taken my (2.5 M) toddler to the pediatrician, and am waiting on a second opinion. The first pediatrician couldn't give me any type of a guess, but is running blood work.

My little boy consistently gets this red/raised/swollen patch of skin that is hot to the touch on the same leg, in the same spot, in the general same shape whenever he runs around outside in the hot weather. He claims it doesn't itch or hurt him, and benadryl/hydrocortisone cream doesn't help it go away. The patch only goes away with rest/cooler temperature.

I've taken note that no matter where we are outside (grass, pavement, rubber playground, woodchip playground, even sand at the beach) his leg will react, so it doesn't seem to be triggered by contact of allergens.

Has anyone experienced anything like this before?