Hi, Mary Jane, and welcome to Psych Central! As Mending suggested, it might have to do with your metabolism. Are you eating enough at meals, though? It could be "fruits and vegetables, etc." are not enough. How about meat? Or other sources of protein? Carbohydrates? I'm of the opinion we need food in all the categories, but a minimum of some.

Do you take vitamins?

I think it'd be a good idea for you to talk to your doctor about it. But I don't think it sounds like you have any psychological eating disorder. But, of course, I'm not anyone trained on such a matter.

I can get tired and "headachy" when I don't eat, too. Please don't worry. I'd be surprised if anything serious is wrong with you.