I usually get them on my legs and torso, but have had them on my face too. It varies. Funny though, I have not had them much since my colectomy, so perhaps the intestinal inflammation "primed" me for them.
I don't know if you can rule anything out, as there can be slow or delayed reactions. But I guess most causes by foods are usually pretty quick. depending on your sensitivity.
I would even make your headache a suspect, especially if it was a bad one, since pain can stimulate release of various chemicals in the body. http://en.wikipedia.org/wiki/Urticaria