That post radiation tiredness is a surprise but it does usually ease off be kind to yourself was the advise I was given.
I didn’t see the help from exercise at first. But it does help. My body needs to get moving before the pain and stiffness goes. So gentle start up. Then I’m fine, a bit like an old car in winter. Slower to start and then let it warm up the engine oil so it is right to drive off. Try to move off too soon without the proper warm up and it splutters and can stall.
in other words try to get some gentle exercise in. You can only but Try. Start small and build up.