I am assuming you aren't taking a ppi or anything. I have colonic inertia (was IBS-constipation) and I can sympathize with the GERD due to constipation. When I am really backed up my reflux gets worse. First I hope you are ok from whatever made you sick. Maybe try some Pepcid AC...I am allergic to it but I hear it does wonders for others. Or try Prilosec OTC and see if that helps. If you are still having problems, then I would see your GI. I hope the Miralax/Amitiza combo gets you back to regularity. Both don't work for me.
Did you experience nausea with the Amitiza at first?