My dad & advanced prostate cancer

Hi there my dad was diagnosed with advanced prostate cancer 18 months ago. It has been so difficult for him as he also suffers from arthritis. It has been being controlled by hormone tablets until now but at last appointment with oncologist his psa level has shot up and so now he needs to begin chemo. He is also being sent for a bone scan tommorow. At each appt with oncologist when asked how he is he says he feels fine and isnt experiencing any pain. However at least 4 days out of 7 he is in bed from morning till night with pain in his back and hips. My mum doesnt know what to do and neither do i, he has also been given very strong anti depressants. 

So stressed and cant understand why he is hiding from the doctors that his quality of life is poor. 

Any advice would be appreciated x