Bad constipation with Parkinson’s

Hi everyone. Been awhile since I’ve been involved. My Parkinson’s has been doing pretty well for 2/3 of a year now with the exception of REALLY, REALLY bad constipation!!! I have been drinking a lot of water(60 oz a day), walking 5 days a week(3-4 miles each day), and trying to eat high fiber foods. Nothing seems to work much. I have taken Magnesium Citrate on a couple of occasions and tried an enema on a number of occasions too. These work for a short time, but then it is the same old, same old thing. I’ve tried Ducolax and a number of other stimulant laxatives. Same result. Not much. Last week I took the Magnesium Citrate again and this time when I drank it I had a horrible burning feeling in my upper GI tract. Had to go to ER. Did CT scan and could find nothing. Saw a GI doctor at the Mayo a few months ago and he had me do some tests and determined that I most likely have Bowl Evacuation Disorder. He ordered evaluation to see if I am a candidate for therapy. I haven’t scheduled that yet. I plan on calling his office tomorrow and request to see him again. I just feel so awful. Constipated most of the time, nausea, bloated, especially in am, and cramping. I wake up every morning feeling very bloated with considerable cramping. This is NOT normal!!! So that is my sob story. Am I going crazy? I am sincerely starting to think so. Has anyone had or have a similar experience? Your input would be greatly appreciated.