Keep busy, and as mentioned, join a support group or get counseling. Certain historic dates do bring back memories, good and bad, like diagnosis date, and NED. Try to think the more positives ones like the clear scan, clear margins, you quit smoking, and you have the rest of your life to look forward to at age 26.
If you are close to NYC there are three H&N cancer support groups, and one in Long Island, that I know about.
Good luck.