Hi Lynn16, welcome to the forum.
It is definitely a mental challenge, from the initial diagnosis to – as you say – the side effects and new normal life.
You are getting well through the treatment. Perhaps focussing ‘on the light at the end of the tunnel’ – the prospect of going into remission – would help?
On exercise, I have been there. I lost a huge amount of weight during treatment, much of it muscle. I got back into the gym when treatment finished: it took so much willpower to rebuild my strength, but I got there!
I agree with Rosary about friends. They probably don’t know what to say. At least they are still contacting you: I had ‘friends’ who didn’t want anything to do with me as soon as they heard of my diagnosis 🙃. It can be a time when you find out who your friends really are.
All the best
Rabbit