I have issues with it on Tramadol. Just look it up on web MD, usually you will find things that you experience are just normal side effects and you shouldn't be too worried unless your abuse is a lil out of control.
Opiates help your body retain water. If you're very sensitive, this could be normal.
However, you should take something that will help your body expunge urine, because not peeing for a long time isn't good, your kidneys will get backed up if it goes on for long enough.