It seems you are doing better than most, what with going back to work already. The recovery is indeed very slow, comparable to a burn recovery in that it takes much longer than a simple bone fracture or sprain. The radiation has cooked your body from the inside. Add to that the Chemo. It seems your team really wanted to make sure you were not going to be defeated by the cancer.
So now you have passed the bottom and are on the rebuild. Yes it takes time. Years in fact as most will attest. The major bad stuff goes away in three to twelve months. The annoying stuff takes years and possibly never goes away. Eventually we learn to cope with the permanent damage, telling ourselves we are alive and what is just is. That of course isn't everyone. Certainly with the advances in head and neck cancer treatments, particularly in Squamous Cell Cancer (SSC) and with a link to HPV, the likelihood of reoccurrence is now extremely minimal.
Check back on your situation in 2.5 months. Then again in 2.5 years. I suspect you will just look back on this as the nightmare it was. Me, I'm 25 years out, but it still feels recent. I probably have lived more in the those 25 years than I ever could have imagined. I believe you will live life to the fullest as well. This journey changes our very soul. You have faced the old man at the door and sent him away. You have met this challenge with courage, which only makes you stronger. I wish you good healing. Find a permanent place for that water bottle beside the bed. Don't forget to smile when you wake up every morning. Congratulations, you've beat this!