Know anything about red bumps in SE Asia?

[emilyoung3]

I just left Indonesia, where I spent three weeks on Bali, Gili T and Flores with my boyfriend. Our second day on Gili T, my boyfriend developed many small, similar to chicken pox, bumps on his shoulders and back (he had chicken pox as a kid). After a couple of days of them not going away on their own, and spreading slightly, we went to the pharmacy and they gave him antihistamines.  We changed the soap we were using, and had our clothes laundered. And checked all of our rooms for bed bugs, as we were moving around a lot- and never saw any. It seemed to clear up, but then a week later, when we were in Ubud, Bali, they manifested on his arms and legs, but were a little bigger, puffier and itchier this time. So we went back to a pharmacist and got a different antihistamine. Then it cleared up.
And we flew from Indonesia to Thailand for two days, and then to Vietnam. On the morning of our flight to Vietnam, he woke up to angrier, puffier, blotchier (but still with very defined borders) bumps on his thigh, and a couple of raised, red, hard, blistering splotches on his calf.
Does anyone know what this could be all about?