I have had a bump behind my right arm near the shoulder.  Its been there for 23 years when I was pregnant with my first child, at that time it was filled with puss.  I just squeezed it out and never thought of it after that, but its been there since.  And now the puss is back.  Its kind of a hard bump and again filled with some kind of puss.
Hi, From history it seems that you might be having infected Sebaceous cyst giving this problem. It is not going to heal unless get it operated with sac. Consult surgeon and get examined. Ok and take care.