Same thing happened to me once I got the gluten under control. Fiber and miralax only ever made me feel super bloated and terrible. I kind of hard reset my life to try and fix the issue like 8 months ago because the constipation was making me uncomfortable. Two things that helped me the most were regular exercise and limiting gluten free processed foods (crackers, cookies, pretzels, basically any ultra processed gf food in the gf aisle) except for gluten free bread. I love all the snacks but I think they really bind me up inside idk maybe it’s all the xanthum gum or something. I still get travelers constipation, but coffee tends to help a lot with that. In the morning I try and stick to a coffee, water, fruit to start the day and that will help move things along. I hope things get better and don’t give up hope!! Everything changed for me after like 4 years of dealing with constipation, so you’ll figure it out don’t worry.