@CLF the radiation fatigue can take a while to get over. Try slowly building up your endurance slowly. Also getting help from a physio that specialises in cancer related issues. You haven’t said whether you are on any on going treatment like hormone blockers. Which can make you a lethargic as well.
I saw a physio as well as a councillor as that also adds to lethargy. Its like a big crash at the end of active treatment. If you have a breast care nurse get in touch with her/him. They are a vital source of info. Also our help line can be very helpful as well.
Check out the various podcasts on here as well there is lots of good ones available to listen to.
I am still struggling to get to a decent level of exercise but for a different reason.
The link to the podcasts are at the bottom of this page
Hopefully someone from Perth area can point you to something in your area Im Sydney based