After treatment for anal cancer I had Xylocaine for topical application esp @ bowel movements (ouch), I also had the usual parade of painkillers: panadeine forte, endep, Actiq, etc blah blah.
BUT nothing really worked because it was NERVE PAIN - what finally did work was LYRICA (an anti-convulsant) 75 mg 2 x p/d.
I read about it in a book called "Manage your Pain: Practical and positive ways of adapting to chronic pain" by Dr Michael Nicholas, Dr Allan Molloy, et al. (c)2000 ABC Books. I highly recommend this book for behavioural strategies, thinking strategies, plain English medical information.
Hope that's helpful, I wish you all the best for your recovery 🙂