Since the swelling is not red or painful, it is probably not an abscess and likely is a swollen lymph node. Lymph nodes in the armpit are at the top of a lymphatic channel that goes all the way down to the fingers. An infection in the fingers, hands or arms can cause swelling in the lymph nodes of the armpit.
Do you have any of these symptoms
cuts or sores on your hands or arms
areas of redness on the hands or arms
new swelling in the hands or arms
recent bug bite on the hands or arms?