What Does A Painful Knot In Armpit Indicate?

I am having pain in my armpit, there is a knot on the inside of my left armpit. Well a swollen area, that seems to be round. On the same arm is a knot located on the right side of my left arms bicep, near my elbow. I don t really feel pain in the knot by my elbow unless I touch it, Its also round but smaller and I can move it. But the one in my armpit is bigger and getting to be painful, this happened about two-three days ago. Would you have any idea what it might be and/or what I should do? I hate searching things on the internet, cause you get everything from it could be caused by deodorant to cancer,torn muscle,etc,etc. Please get back to me soon and thank you.