Beautiful picture ...Lone Pine Lake, right?
Most important: Next time, go when you don't have any fever issues.
If you were urinating that often, I'd say you were over-hydrating. There IS such a thing as hyponatremia (too much water without electrolytes) that can cause a headache. But you were using electrolytes, so that probably isn't it.
The headache is likely due to altitude. You sound like a candidate for Diamox, and more acclimatization: Spend time higher and longer next time -- maybe check out Horseshoe Meadows and try hiking around there.
