Any idea what this rash is?

[Dilbertian]

13yo ds has a rash on his inner thigh, and a little patch on his lower back as well. He showed it to me last night when it started itching him, so I gave him an antihistamine. Today the rash looks like tiny blisters, and there's a new patch below the original cluster of patches. Any idea what it might be? Is this a trip to the GP?

GP said shingles. Off school until it's all scabbed over. It's clearly shingles now, as the rash has blistered dramatically. It's still spreading, but ds is otherwise entirely well, thank goodness.

Shouldn't need to stay off if it can be covered. Only passes on chickenpox with direct contact with fluid from the blisters