I have slow transit constipation and ibs. So I rarely have diarrhea. If you have overflow diarrhea maybe slow down on the miralax..this can cause lots of diarrhea as it is also used to prep for colonoscopies. But your issue may be different especially if you're not taking as much. But you can also cause diarrhea from doing a little too much of everything to try to get things moving. I'm not experienced as much with that area. A diet change, food sensitivity trial could be good but it can be overwhelming so I'd recommend a dietitian to help you. There are other certain diets you can try just look them up. Low fodmap diet, gluten diet, inflammation diet, ibs diet. Hope you figure something out! Remember to hydrate if you are having lots of diarrhea.