Dealing with withholding and constipation in 3 year old. What treatments other than Miralax worked for your kids?

EV

We’ve tried everything with diet and have not had much success. Our 3 year old is going every 3-4 days and they are HUGE. I’m worried she’ll get megacolon so we’re looking into laxatives or stool softeners with her next peds appointment. What worked for your little ones?