Movable painless swollen lymph node in armpit its been there for 5+ years i believe had ultrasound doctor request biopsy to be safe i'm 18 cancer?

Unlikely: If the node has remained unchanged in 5+ years, it is not likely to be cancer. You may wish to get a second opinion before opting for biopsy, as it may not be warranted.

Not sure: if it has been there for five years and hasn't changed that may be a good sign. saying that, go see a general surgeon for further work up and consideration of fine needle aspiration and or biopsy.