What Casues Numbness And Tingling Sensation In The Left Armpit?

Last Thursday I had done some yard work. Nothing out of ordinary mowing, edging etc. That same night I felt as if I had strained a muscle in my left shoulder. I applied a salon pas and tried to rub it out. By Friday my shoulder muscle was still bugging me, but by dinner time I noticed a tingling/burning maybe a numbness/itchy kind of feeling in my left armpit and down around the upper part of my arm. It s hard to describe the sensation. As, of yesterday evening I noticed the irritating/itchy, burning sensation come across the top of left side of chest just above my breast. I did notice that my left underarm seems a bit swollen in comparison to my right underarm. I don t feel any significant lymph nodes in either underarm. I feel no lumps in my breasts either. I just had a mammogram about 3 months ago, results were fine. Any thoughts are appreciated....I ll be contacting my family Physician in the morning.