I have lump of soft tissue under my arm...and experience random stitch pains just above my left collar bone and just under my left ribs...exactly like the stitch pains when you do lots of cardio and your unfit..

Axilla lump: A physician would have to examine the armpit lump in order to make a diagnosis. Possibilities include inclusion cyst, enlarged lymph node, benign fatty growth (lipoma). The random pains you describe are quite nonspecific & could be irritable rib cage muscles or pinched nerves. If they persist see a physician for evaluation and advice.