Chronic migraines from the sun?

For the last few months, I've been getting really bad migraines from the sun. I've mentioned it to my doctor once, but not while it was severe as it is now. They just suggested that I might be dehydrated and that I should try drinking more. I would agree, except the migraines happen almost immediately. If I'm outside on a sunny day for more than five minutes, they start to flare. Is there a medical condition with as symptom like this? Does anyone else struggle with it? Does anything help?

Edit: I'm glad to see I'm not alone in this! Thank you everyone for the suggestions. I'll definitely be trying some out.