What Causes Swelling On Neck From Collar Bone To Jaw Bone?

Have a large soft swelling in the right side of my neck now reaching from the collar bone upto my jaw bone. its painless dont even know its there unless I feel it I did go to the doctors last year saw 2 doctors and they said its nothing to worry about but it is still getting bigger, I am getting really worried now as there has been alot of cancer in my family and I am quite scared in case it is cancer.