What an unpleasant experience.
When a drug that is meant to relieve you of pain is not doing so, the worst part is when the doctors can't really give an explanation of what is happening.

The thing about this medications is that doctors are always aware of another option but every drug comes with its own side effects, so they tend to prefer to opt for drugs with minimum side effects. One thing I have noticed is that the stronger the drug, the greater the side effects. I'm just glad you survived this ordeal.