My son has had this weird rash that comes and goes on different parts of him. It's red with a white blister in the middle and sometimes they're quite big and sometimes they're quite small. Sometimes there's a few small ones together, sometimes just one on it's own. He's had them on his face, neck, back, arms, legs...everywhere! Has anyone experienced this before? The pictures aren't very clear. He's also had a cold for the last week or so, the rash has been coming and going for the last four or five days. Thank you!