I may be a different sort of voice here... I'm going to say that it *Might* not be depression. I say this because you described something very similar to where my Mom is. She is 57, and also was very active. She has days where it's all she can do to make it out of bed. I heard you say what I have been wondering all along... "I thought people had better days than this. Is this not normal?"
Definitely be very up-front with the onc. about all of the things he is feeling, explore the possibility that depression could be contributing... but also realize that might not be 'the answer' and though I can't offer any suggestions, I will at least say--Me too for what you are seeing, and even perhaps what you are feeling. I am so joyful for those here who are still able to be active and up and involved in life. My mom is not physically able to... and it scares me that her 'normal' looks so different than the 'normal' I have heard about and hoped for for her.
Praying for you and your husband. (((hugs))) to you.