It sounds like it could either be a swollen salivary gland or a lymph node. Because I'm unable to see her to figure out which one, I think the best thing to do is to is to have her seen by her regular vet again as soon as possible. They may opt to do a FNA (fine needle aspirate) on that lump to see if it's a salivary gland or lymph node issue.
At the very least they should run a little blood work to make sure there's no underlying infection or some other disease or illness such as cancers or even allergies that can cause those glands to swell.
Because she's still pretty young, I don't think I'd be worried about things like cancers or anything just yet, but it's best to have it seen sooner, rather than later, just in case.
Hopefully it'll just be a bit of an infection going on, but it's always better to have anything involving the throat/neck checked out, since it can compromise the breathing if left untreated.
It's also unlikely that it was caused by an injury. If there was a neck injury I'd expect the neck itself to be swollen, not the glands.
I hope this helps.
Since he's on Metacam (which is an NSAID...like aspirin) that controls pain and helps with swelling and Tramadol (which is a synthetic drug in the morphine family) which controls pain, and still seems to be getting no relief, I'm even more convinced that he's got some kind of infection, rather than just pain.
Infections don't get cleared up by these kinds of pain medications, to get an infection under control you need to use an antibiotic. Having the vet do some blood work to check for infection would be the first step I'd request from my own vet.