Well the thing is a lump can manifest for any number of reasons. It could be a little ball of fat, really anything. But if you've just discovered it in the last little while you're not in any immediate danger. What I would do, is ask your doctor the next time you talk to him to do an xray of your chest and/or neck, to get a better look at what's going on. You can even have a biopsy done (which is a peice of cake, i've had a couple) where they remove the lump and send it off to see if its cancerous.
As of right now though, I don't think you have much to worry about. I know the waiting and uncertainty is the hardest. But just remember, even if it is something, you've caught it early, and it takes a long time to spread into your lymph nodes. My father had cancer for years before he dragged his stubborn butt to a doctor and it had only entered a few lymph nodes, even after his neglect of a big red oozing thing on his chest for 3 years.
Just stay on top of it, and I know you'll be just fine. :)