There are many things it could be and your doctor is the best to discuss it with. I had a lump in my neck that was not sore but I noticed it when I put my seatbelt on - it seemed to be an irritant right at that spot.
After a number of tests including needle aspiration of the lump (turns out there were two), I was diagnosed with Thyroid cancer. I did have surgery and followup radioactive idodine. But all along the way, the vast majority of the kind of lumps I had are very often benign. In any case, it's best to see the doctor -- hope yours is determined to be benign!