Diagnosis of Anal Cancer

Hi, I’m now over half way through radiotherapy and chemotherapy.  Struggling a lot with side effects so in a lot of pain when going to the toilet.  I have been prescribed 2 different types of gel and taking paracetamol but not working.  I spoke to a radiographer today who is going to prescribe codeine, I worried about taking this due to fear of becoming constipated as this will effect treatment, I will also be prescribed laxido.

Is anyone else experiencing anything similar or have advice on any self help techniques?
I have been informed the pain will continue post treatment whilst things slowly get back to ‘normal’.