My 2 year old keeps saying the back of her neck at the base of her head hurts. There doesn't seem to be any tag or bite. What could be the cause?

Back of neck hurt 2y. The back of neck hurting in 2 years old probably is nothing serious as long as it does not continue, 2years old are active and it may be a muscle pain. You can give tylenol (acetaminophen) or motrin, and if persists see your pediatrician to have her checked.