What Causes Persistent Lump On The Left Side Of Neck?

I had a small pea sized bump on my left side of my neck about a yr and a half ago. Just above my collar bone. My dr told me not to worry. No I have had unusual discomfort after working out on that side of my neck and upper chest. The area above my collar bome is slightly larger than the right side and is hard when palpated. Should I be concerned?