I have found that I needed to stop the Zelnorm for weeks before starting it again than each time I take it, it becomes ineffective even faster.
I would suggest not taking it for at least a week. During that time, double your dose of miralax and see how you do. Remember to take the miralax on an empty tummy, shirtly before eating. I've found that it is most effective that way. Of course you need to drink plenty of fluids through out the day for the miralax to be the most effective! Good luck!
-------------------- Taking it one day at a time.....