Eating that causes pain - Sticks to Organic diet as much as possible

Whenever I eat food if it is " conventionally " grown/raised I often have sever muscle spasms in my neck. Same spot everytime. The pain is often irritated by sitting on a computer/using devices however it feels directly related to eating. If I go without water and food all days sometimes food for days the pain goes away. At times the pain gets so great it becomes a main focus to get rid of and I would like to figure out someday the cause. I found bottled waters can even cause this it seems depending on their source. I would like to test the components to see if there is a possible link to phosphates and the muscle spasms. Going through holidays not eating gets old but its alot better than writhing in pain.