Vegetarian Headaches?

Having been doing this vegetarian thing for a little while now, I’m still trying to figure out what is what in the nutrition side of things. I’ve noticed I get headaches a little more often than I did before.

Still trying to isolate what could be the cause of it. A lack of nutrients? Or my exercise level? I started running a little more than I did back during my meat eating days. Lack of water? Stress from the job? Could be almost anything really.

I try to avoid popping an advil for any old thing, and I notice that my headache goes away usually once I get a little more food in my system. They aren’t killer ones either, just a dull ache, pulses slightly.

Anyone have any thoughts or opinions on that? Again with anything in life there could be a million reasons why. Not quite sure if I can pin it on vegetables, or a lack of a certain something. I appreciate any advice.