Swollen Glands to Back of Neck and Hives

This is the second time in 2 months that I have had large swollen glands to the back of my neck followed by hives to my truck, stomach, arms, and chest areas.  I can not think of anything that could be causing a allergic reaction.  Also, my Right hand, fingers, and right foot are swollen.  The joints also feel very sore.  My doctor prescribed Predisone the first time and it resolved.  I'm just curious what is causing this symptoms and is there anything I can do to prevent them.  I personally think it is stress causing it.  Thank You!