I absolutely understand where you are coming from. Radiotherapy is gruelling.
There's no set time on when you'll feel 'normal'. As the weeks and months go by you'll notice little changes, such as feeling a bit better or feeling confident in trying something challenging to eat. You will have a few set backs, when your body doesn't want to do anything except sit or sleep, and it doesn't want to eat any solid foods, but that's OK. As long as you are drinking plenty of water (2 litres) and getting 2500 calories (with around 90g of protein as it helps the body heal), you'll be grand. Try to do a little exercise every day, even if it's a 30 minute walk or going up and down the stairs 10 times in a row, it'll help massively.

13 months from my surgery I'm feeling well, but I still have days/hours where I'm tired or I just don't want to eat solid food, or I just feel down. What we've gone through is traumatic. The surgery is brutal, and we all need to accept that there isn't a time limit on recovery, including that of the mind as well as the body.

Your recovery will depend on you, one day at a time.