How To Get Rid Of A Swollen Lymph Node In My Right Armpit?

hi i am 16 years old and i have had a swollen lymph node in my right armpit for about a year now. I had it checked by a doctor when it first developed but it is still there. its about a quarter in size, absolutely painless, and only swells when i get sick. other than that i feel completely healthy and the lymphnode does not affect me in any way. what do you think i have?