It can be an allergic reaction, a swollen lymph node, or a cyst, It could be an infection pocket either way if it gets bigger than a dime, has irritation, redness, or just plain hurts, get it checked. Otherwise it may just regress, get smaller and go away. Again, if it gets larger or hurts badly or turns really red GET IT CHECKED
I Have A Painful Swelling In One Armpit. Recently Had A Flu Shot. Swelling Is Visable To See In Mirror.What's Wrong?
It can just be your way of getting used to the flu shot! Or it can me an reaction call your doctor and like him the the affects!