Should i be worried about a pea sized bump behind my ear that doesn't hurt or move?

Likely not: "Lumpy bumps" behind the ear, and under chin known as lymph nodes swell usually with infection or inflammation. Since yours is pea sized and not getting bigger, it is probably a lymph node and as such normal. Keep an eye on it, if you start getting pain, it starts getting bigger or you start noticing other lymph nodes in other places, see your doc as lymphoma would be a consideration.

At 18 , no: but still need to be checked by your doctor . Most likely you have a cyst more common at your age . Make sure to see your doctor and once cleared , you don't have to worry .