I am 24 years old male and I have a lump type swelling near my armpit. Not exactly armpit, but like 4 fingers below the armpit and its on the back side of the body. I found it when i was watching a movie on my laptop lying down. I felt pain and when I touched there I found it. At frst I thought its muscle cramp or something. So I stretched my hands forcefully, and it went away. Later it come back again within hours. I did the stretching again. It was going away. But one time it didnt went.. And It was like 2-3 cms large and hard. It was freely mobile. I went to a physiotherapist. He told me to go to a physician. On going there I was told to wait for a week. I waited and it shrunk again. On touching there I can feel sac like empty structure. When I lie down or walk, it swells up and it feels hard and mobile. But when I press it gently or just sits down or stretch it goes away.
I am worried. Please help me in this regard.