Any ideas what could be causing this reaction?

Tuesday night i noticed my son scratching his thigh while i was feeding him. I pulled him out of his chair and lost my breath when i saw his legs!

That was the worst patch. Then it spread to his other leg, stomach and neck. I called the doctor and explained it to him. No fever, no vomiting, he didnt seem uncomfortable aside from it itching.

The after hours operator said theyd have the doctor call me back as they couldn't get him on the phone. I called my boyfriend and told him to hurry home then i sent the picture to my mom & two of my aunts. They all said allergic reaction. The doctor called back and i told him the same thing i told the operator, but at this point they were mostly gone. He said allergic reaction and since it was basically already gone to just give him some benadryl & keep track of what hes eating and touching.

I checked on him often throughout the night and they didnt come back.

I checked on him a few times yesterday while i was at work and my aunt was watching him. No sores.

I car pool with my cousin, my aunt wanted to go to the mall right after my cousin was off so we just met there since i needed a few things also. I saw my aunt come in and she sat at a table and started digging through his bag. They were back. They werent there when she put him in the car but they were there when she got him out.

Gone within 30 minutes. Didnt come back all night.

This morning he had two little marks on his face but thats it.

No diet changes, no detergent changes, no new lotions, perfumes or cologne for my boyfriend and i.

Im completely lost on what hes reacting to.

Any ideas?