Kreaybutt
I buy Olympic Organic Probiotic (I'm in Canada, don't know if it'd be available elsewhere.)
Not all yogurts are created equal- all you need to look for are "active bacterial culture" in the ingredients. The bacteria culture that is best for the colon are: lactobacillus and bifidobacteria. My particular yogurt lists these as well as several other active bacterias, but not all yogurts will have as many or list them specifically. If they don't list them, check on the product's website to verify.
I'm planning to make my own yogurt using Olympic brand yogurt as a starter. It'll be cheaper since we eat so much of it.
This site has some information specific to probiotics effect in the intestines http://www.powerofprobiotics.com/Probiotics-for-constipation.html
After using Miralax, laxatives, (maybe even magnesium too) they can cause damage to your intestinal flora, so its super important to replace it with good probiotics.
I can certainly understand the changes pregnancy and birth put your body through! I think it was my 2nd babe that caused me on-going fissure issues.
But ya, pay lots of attention to when you think you 'might' be able to go at other times of the day, and before bed, and see if you can (without pushing of course). Like I said, I squat (since sitting on the toilet for long periods of time isn't recommended) for about 10 minutes every evening before bed, (sometimes without an urge) and usually my body responds to that action and getting into the habit of an extra BM.