Is he sluggish or fatigued? Falling asleep or hard to rouse? If he is take him in.

He sounds a little dehydrated. You can give him water or offer more BF.
Icy poles are great for this too - Frozen Coke was the only way Charlotte survived the Black Saturday temps in Melbourne a few years ago (she was one).
I would call the chemist and check what age they can have the Hydralyte Iceypoles from, and grab some of those.

Keep offering the breast though, and make sure you are hydrated.

But if he is floppy, non-responsive or otherwise listless, take him to the hospital.