What Causes Swelling And Pain In Arm Pit?

At work yesterday I was having a weird pain under my armpit and I had to keep adjusting my pants below my right hip becasue it was hurting. When I came home I felt my armpit and it was swollen also my side above my right hip was hurting and tender to touch. Today it sends a sharp pain if I gently press on my side and the swelling is still under my armpit. I just need to know if this seems like an emergency or what it could be. Also, if I should just wait it out.