22, male. hard lump, 1cm wide. under the skin of the neck on the right side, close to where the skull meets. no size change in a year. sometimes aches

Probable cyst: It sounds to me like you might have a sebaceous cyst. These are generally not serious, but can sometimes become infected, which may account for the occasional aches. The fact that it has been stable for 1 year is reassuring but if it were to change in size, shape or consistency or to form an abscess you definitely should be examined