It is that open ended question with an open ended answer. The pain may have started with an injury to the area or maybe you woke up to find yourself in pain. " I have no idea what caused this to hurt so here. It just started one day!" But with no injury, how does one explain the pain or the intensity of the pain.
The pain has now become chronic. The question is what are the sustaining factors that help maintain the pain? We forget that with pain we alter our movement patterns. We begin to protect the area from pain but limiting how much weight we let a sore limb bear or restrict normal range of motion. The pain may come as inflammation which is redness and heat. It may be experienced as coldness or restricted circulation. We may also hold our breath in anticipation of probable pain. To make things more painful, life throws more stressful situations to your daily life.
Are you beginning to understand the complexity of the question: "What causes my pain"?