What to do if i have a really short neck and it's been bothering me for a while. is there any way to lengthen it?

No: there is really no way to "lengthen" the neck in a skeletally mature adult. Even when we use traction, the minimal lengthening of the neck that occurs is not long standing. If you are having a lot of pain with it, the bigger question is to more precisely determine where the pain is coming form, as having a short neck is not in and of itself usually associated with pain. consider being seen.