What Does A Lump On Scalp Indicate?

My daughter who is 13 found a knot on the back of her head on the right side. She says it is very sore to the touch. I can feel the knot, looked on her scalp. There is no redness, no irriated hair follicles to the eye. She has said she hasn t hit her head or can remember anything to cause the area to be sore. She has complained of headaches. I know lymph nodes are located in this area. Just a concerned parent. My child doesn t usually complain about things.