I'm no doctor, but I can tell you what was done for me. I had a similar lump, but mine was more underneath the jaw. When I first noticed it you couldn't see it, only feel it. I went to the doctor and was told it was probably an infection. After a month of ineffective treatment, it grew to the point where you could look at me and see it. That's when they started talking cancer or branchial cleft cyst. Frankly, the pictures I've seen of cysts, look a lot like yours.
Anyway, I think the only way you can tell for sure is needle biopsy. I had a CT first, then a ultrasound guided needle biopsy. Turns out I had a baseball size, swollen lymph node and SCC.
I'd get it checked out ASAP.
Tom