what foods are you eating? and i suggest not taking miralax. why did you cut back on fiber?
are you eating or drinking anything acidic? Coffee, tea, tomato, orange, peach, etc? if consuming anything acidic, stop. Try a different acid reducer like Nexium or pepcid.
The trick with IBS is to figure out what causes issues, this will work for reflux too. Keep a journal of everything you eat and drink. then keep track of how you feel as far as stomach and reflux goes.
I'd also suggest finding a good nutritionist. GI are of little to no help if your problems are food related.