most probably it is a swollen post auricular lymph node.
If it is hard and pea shaped, it may be a cyst. Often they may take on the same color as the skin around it until irritated, then they may become a little red. As the cyst grows it may become painful. Things like laying on your pillow may make it tender due to constant contact with a surface that places pressure on the forming cyst. Cysts are caused by a number of different things of which none are anything you should be too scared about at the moment. Often, if left alone they may go away. Applying a very clean, hot compress against the cyst a few times a day for about ten days may reduce the size and even completely get rid of the cyst all together once the fatty tissue has been loosened up and returned to he blood stream. Try that. If the lump is obviously infected, broken, bleeding or not subsiding after simple home remedy treatment then please go see a dermatologist.
Hope that helps.