Sorry to hear about your question. In general, it is always best to speak with your doctors
if you find a new growth or have any concerns about your overall well being. There are many possible things that could explain this problem, some of which we can review here. You could be quite right that you have a minor skin infection similar to what a person gets when they have a pimple. These can grow to be large because of the fact that they are out of the way behind the ear. Other options include similar infectious diseases that involve either the skin or even the deeper aspects of the ear and the bones associated with the ear. Usually patients will have some ear or hearing complaints in these cases. Skin disorders are also often found in this region, with sun exposure over a prolonged period contributing to the development of some of these. Additionally, allergic reactions or irritation from glasses can sometimes play a role in the development of some lesions. Due to the location, it is important that you have this evaluated by a doctor to make sure that there is nothing more serious going on. Please speak to your doctor.