What Causes Swelling In The Collar Bone?

I have a swollen area above my collarbone. My doctor says it isn't my lymph nodes and doesn't think it is anything to worry about. I have had it for a week, its a bit tender, probably because I keep prodding it. I suffer from Health Anxiety so naturally I am worried. I started going to an exercise class about 3 weeks ago and remember thinking how sore my neck was a few days after, so could it be swelling from this?