Amytripyline withdrawal or gabapentin side effect or neither ?

Hi everyone not sure if anyone can help … my bladder consultant has Replaced my amytripyline with gabapentin to see if the charge helps my retention issues … I was only on 10mg of amytripyline so thought nothing of changing though I did check with pharmacy first … it’s a week tommorrow and apart from outrageous thirst I am being plagued by horrendous headaches that nothing is touching … I am now wondering if I’d have been better withdrawing amytripyline properly instead of just swapping as I am not entirely convince the pharmacy assistant at hospital was paying much attention when I asked how to switch as she had a very long queue !

Anyone any experience of stopping amytripyline or starting gabapentin and had similar symptoms ? If so any tips ?