What Causes Painful Lump In Armpit?

Hi, I have a very humongous bump/lump in my armpit. It started off very small and has grown in size over a 2-2 1/2 week period. Sometimes it can be very painful to the point where i cant move my arm and im crying. Other times it is not that bad. What do you think this is. I also have the same bump/lump on the edge of my other underarm. it causes minor pain and irritation, but i have not seen it grow. My mom thinks they are risens . I dont know what that is. Im not sure if it a cysts, or a swollen lymph node. I just dont know. HELP PLEASE