What Could Knots On Elbow And Neck Suggest?

My daughter is 31 years old. This week she had a rather large knot come up on the inside of her elbow. In the past few months she has had a knot come up on her neck..comes and goes. She has had some nodules come up on her inner thighs as well. Dr. told her today he has NO IDEA what it is....xrays showed nothing.