What Causes Severe Pain On Backside Of Head?

After a morning of being lactose and sitting on the toilet my body was very stiff. I moved my neck and felt something pull in the back of my neck, and afterwards a huge sharp pain in the back of my head. I had a headache where it made me unable to move until it settled down, and over the period of 3-4 days the pain was almost gone completely. Today I had another stomach ache, and my headpain came back completely. It throbs in my neck like I can feel my pulse, and hurts the back of my head per throb.