I agree that it could be a hydration/electorlyte issue. Perhaps you should experiment with drinking your electrolytes rather than taking the capsules. I get kind of jittery when I've uses capsules before. I now stick to Cytomax.
I'm also curious as to what kind of sunglasses you're using. Do they offer any glare resistance? I know that glare used to both me until I invested in some Tifosi sunglasses that protect against it. My eyes don't bother me nearly as much now.
I also found myself getting post-ride headaches when I first started riding again this spring after the winter hiatus. I started taking some Excedrin the minute the ride started and that did the trick. Eventually, I found myself forgetting to take the Excedrin, yet I stopped getting the headaches. I haven't otherwise changed any of my eating/drinking habits, so I tend to think that I was just readapting to riding.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher