What Causes Swollen Lymph Node Under Armpit?

i have a swollen lymph node under my left arm pit, has been there for a week and getting bigger. i have had problems woth this every month another very painful lump. i only get it on the left side. in the course of three years i have had over 30 abcesses/lump under the same arm. 3 had to be cut open...im concerned it may be more than just a lymph node swelling up due to infection..should i worry?