What Are The Side Effects Of Long Term Use Of Polythylene Glycol?

I saw a Dr. 8/7/2014 and was diagnoised with Gastroparesis. The next appointment he put me on three capfuls (51 grams) of polythylene Glycol 3350 once a day in 8 oz. of liquid. I was in a hospital and had severe constipation. That was in September 2014, since then, I have cut the amount down to two capfuls and now on one. I am having stomach issues and he is going to do an endoscopy on 2/10/2015. I have heard different doctors say you could not take too much of this medication. What is the danger of staying on this for a long period of time?