I have had this lump in my neck all my life that fits the description of a swollen lymph node. the doctor says its harmless but swollen lymph nodes are only suppose to last like a few weeks and i've always had it. what should ido?

Some : Some lymph nodes are bigger than others, and if this has truly been stable throughout your life, then it's not something to worry about. Lumps in the neck aren't always lymph nodes. There can also be congenital cysts of various type that look and feel like a node but are actually just contained fluid. Again, the long-term stability of this in your case would argue pretty strongly against it being anything bad.

Not a lymph node: Lymph nodes swell when there is infection present somewhere in the vicinity. After the infection is cleared they will return to their normal size.

LN can stay big: Sometimes after a lymph node has enlarged due to an infection, it doesn't return to its previous size. I have two that got big when i had pneumonia over 20 years ago that i can still feel. I'd be more concerned if they were new and getting bigger, but if you've had them for years and they're the same size, they're probably nothing. If you're still worried, tell your doc.