hello greeneyedcat and you are very welcome, we have a breast cancerish title, but anyone who has been affected by cancer is very welcome 
It sounds as if you have had a very tough year, it's great you have had your first all clear, but the deflated feeling you describe is very common, somehow when you are having pretty intensive treatment you sort of keep going and deal with the physical effects, and that can mean the reality of it all goes on the back burner, but when the treatment intensity decreases it all hits you again.
I don't know very much about anal cancer, but I think it is one of the more uncommon cancers? that must make it very hard in terms of finding others in the same boat for mutual support, and in terms of gaining info., it is very hard when you feel you are going though it all alone. I hope we can support you on this thread. I can sympathise with the damage that is caused by treatment - I had breast cancer, but chemo did a lot of damage that I am still recovering from now.
I think its a process of almost grieving for the life you had pre cancer, and finding a way to live well and happily with the 'new normal' the new way your body is, and that can take a lot of adjusting to. And in actual terms all this is still very recent for you, so don't panic and think it will never come right - it just takes a while - moving further in time from DX helps too.
Hopefully some of the other women on this thread can talk to you more about the specific effects of radiotherapy, I have found that the pain and nerve damage from surgery and radiotherapy have gradually settled down (I am five years from DX) and I certainly feel much better now than I did after 18mnths, so I would hope that things may improve for you too. Meanwhile have a
and some
and welcome 
marshy - hooray for good news, so pleased for you 
Ruby - no wonder you are feeling rough, that is very low - hope they can sort you out asap xx