None of the health problems that you are having currently explains this tender bump that you have developed. It is essential to have a look at it and to feel it to make a diagnosis. Based on its location I would consider possibility of inflammed lymph
node. other possibility is that of something like insect bite and resulting itchiness, swelling and tenderness. Sometimes there can be stretch of muscle/ tendon / ligament at the base of skull which can cause such pain. The pain in the left ear may be related to the same pathology as that of left skull base.