Suggest Treatment For A Large Knot Appearing On The Clavicle

I have a fairly large knot, that feels like hard muscle on top of my clavicle (in between my neck and shoulder). Its been there for a little over a week. Last night my husband tried to massage it out, and now it is in more pain. I'm wondering if I did something wrong while doing weights, and if it will go away on its on. And how to get it to go away?