I Have An Egg-sized Lump Or Knot In My Upper

I have an egg-sized lump or knot in my upper triceps muscle. I noticed it about three weeks ago. I had been skiing four days, and the next day I noticed a bruise on the medial side of my upper arm. It wasn't painful or sore, and I have no idea how or when or what may have caused it. I noticed the lump at the same time. The bruise grew in size until it was just below the armpit to a third of the way down my forearm, and then went away over a week's time, but the knot is still there. Any ideas?