That can't be nice for him - RT -it's a tough regime. Where is the source of his blood? The 3rd week onward can be very trying for RT patients and what you describe is not unusual.
He needs a doc/consultants opinion on what to take for relief. Oral morphine - morphine patches. Only the medics can give the best advice.
The next few weeks are tough sad to say. That's RT . Make sure he takes plenty of fluid and nutritious drinks etc. I presume he has had some type of feeding tube put in?
All the best - tony k