Caffeine does not effect me either, so I can understand that it is probably not a factor for you either because you have been drinking so much consistently for so many years. I try to stop it by 3pm, but I will have the occasional one around 8pm. I usually drink about 7 cups a day and it doesn't prevent me from napping 4-5 hours a day or sleeping at night.
I guess the Doxepin isn't working for you anymore. Do you think you need to take it if it isn't working? I wouldn't bother… why pay for it and put it in your body unnecessarily?
Doxepin was an out-of-the-box treatment that worked well for a while. Maybe your pdoc has something else up his sleeve that could work? It couldn't hurt to ask.
I want you all to be well, and I worry when you guys can't sleep