Hi I have had a lump in my armpit for 3 weeks. It started small but grew in size until it became very sore and swollen with bruising type pain down my arm. I visited an urgent care and saw a nurse who said it was likely an infected sweat gland or hair follicle . She prescribed amoxacilian (sp). After a couple of days taking them the swelling and lump has gone down but my arm is still sore and achey and now I have what feels like a swollen vein or tendon raised up in my armpit heading down my arm. It is very sore to touch and my arm hurts if I raise it or attempt to reach. I went to have an Ultrasound done and the Dr said that it was a sebacious cyst - the problem is that the pain is radiating down my arm and the swellign is not getting bigger, so that it cannot be ruptured (even with heat and campophanique)