HI Amy- I'm no doctor, but my kids have had experience with Miralax and I've had lots of conversations with doctors about their poop routine, etc.
Some people are very firm believers that people must poop at least once per day-if not, you're constipated! Others, including some doctors, believe that everyone has different schedules for their bodies, and as long as there are no problems caused by not going daily (e.g. soiling, pressure, bloating, loss of appetite) then don't worry about it. I agree with the latter group.
One of my daughters, now 10, has had issues with withholding her poop. We started to give her Miralax, at the advice of her pediatrician to make the poop softer, and harder for her to hold in. (She'd been having accidents. X-rays showed she was full of poop. Her belly was distended, and she couldn't eat much because there was no where for the food to go-literally that full of poop!). She did start going more frequently, but still having accidents. So we were referred to a gastroenterologist. They were obsessed with "getting her cleaned out", and if she wasn't going every day, then she MUST be constipated!!!!. So, we gave her more Miralax. She had more accidents because her poop was sooo loose she just couldn't hold it in. A rather embarrassing problem for a 10 year to have.
My daughter kept telling me that her body just wasn't giving her a signal when she had to go, and that's why she kept having accidents. She asked to have the amount of Miralax reduced, but I was sure the gastro. doctors were right. They're doctors after all, right? Well, I finally listened to my daughter, and gave her less Miralax. The accidents have nearly disappeared. She typically poops every other day, and that seems to be just the way it is.
So, long story short, "if it ain't broke, don't fix it". I wouldn't worry about your pooping habits. Yes, Miralax now and then should be fine. That's what it's for. Too much, and you'll be sitting on the toilet all day, so don't overdue it to try to make your body do something it doesn't naturally want to do.