What Causes Headache, Nausea And Stiffed Neck?

Hi, I am a 28 yo female approx 5 6 and slightly overweight. I have noticed recently that I have been getting headaches, nausea, and a stiff neck. My symptoms are generally in the afternoon and will go away about 15-30 mins after I eat. At times my symptoms are so severe that I can not drive until it passes. I do eat through out the day and feel that I stay hydrated. Any idea what might be going on?