Bowel Issues

Okay so I've had my first ever experience being constipated recently. Was taking colace daily for ~7 days no luck. Used a capful of miralax and was able to go. Now it's been a full 48 hours since Miralax and I'm having stomach cramping abd diarrhea? Is this still the Miralax?? I'm going to he 35 weeks if that matters at all?