I Have Had A Swollen Lymph Node In My Armpit

I have had a swollen lymph node in my armpit for over a month now. I went to the doctor and he said there were no signs of malignancy because of its feeling. He did blood work and all my blood levels came back perfect, thyroid and white and red blood cells. He also tested for mono which I have a reactivated infection of. It was the Epstein Barr test and it came back off the charts. The normal was 18 and mine in the 500s. I am wondering if this is normal or if it something to be concerned about. My doctor said to come back in a month to check it out but I am just wondering if I should worry or not. Thanks! I am an 18 year old female if that helps.