I believe it could be the sun because it does the same to me. My md calls me "sun allergic." Here's what helps me:
Avoid the sun whenever possible. I even had to stop attending my son's night football games because the stadium lights did the same thing.
I got my car windows tinted as dark as legal.
I wear spf 70-80 everyday and reapply if I go outside.
I turn off the flourescent lights at work and use indirect lamps.
I wear dark glasses, sometimes inside if it is bright.
SPF clothing. I even found a hood that is spf 50 on the campmor website. It is great for driving, which I do a lot of.
If I do have to be outside, I cover up in spf clothing, wear sunscreen, hide under an umbrella, and hide in the shade as much as possible. 15 minutes in the sun can put me in bed for 2 days.
Some of these may sound extreme, but once you experience the toxic affects, you don't want to repeat it!
Hope this helps!