Hi Jon,
There are a few folks on this forum that have been seen multiple times. Most have sought the opinion of several different doctors and ENTs, been scoped, poked, prodded, scanned and tested and some even biopsied. The results have been negative like yours. I know for me, I would have been jumping for joy had I gotten the results you have and given your age, I'd be out and about and living large I assure you!
There comes a time when you have to accept the opinions of trained professionals. Sticking your finger down your throat and constantly prodding and squeezing your neck and gland is not helping.
The anxiety your feeling due to thinking about this being oral cancer can be detrimental and cause issues and complications that aggravate your overall health. As this has gone on for a year and several doctors have given you a clean bill of health, I suggest you discuss your fears with your GP and have him recommend someone you can speak to about this.
Good Luck, positive thoughts and prayers.