So sorry to hear all this…sounds like you have every comorbidity. The exhaustion impacts any motivation to move.
I had DCIS - I treated with high dose radiation for one week and yes a lot of fatigue and later some tightness and discomfort in the breast and axila and shoulder. Physical therapy helped a lot with that discomfort and the fatigue went away after a couple months. I chose not to take AI because I did not want to spend the next 5 years back in menopause. Whether or not that was a good decision we won’t know.
Have you considered taking supplements like B-12 or at least asking your MD to check for inflammation markers. Also PT could help with energy levels as well by getting you moving therefore increasing blood flow and circulation.
Good luck with your PCP or oncologist getting them to address those issues.