What Causes Diarrhea Along With Abdominal Distention?

In late October, I started with symptoms of gassiness, watery stool, distended stomach which then led to worsening symptoms. Approx 2 weeks after symptoms started, I was in a lot of pain and went to Urgent Care. An x-ray showed that my right side was filled completely with stool, air on the left. I was sent home with a bottle of citrate of magnesium which helped produce a bowel movement 12-14 hrs later, which was very productive. Symptoms were better but I was still not normal and symptoms then again returned approx 3 wks after that visit which another x-ray showed the same. I went home with Miralax and dyclosine which seemed to make my symptoms worse along with another bottle of Citrate of magnesium, again producing bm. I didn t think I was constipated, because I d been having bm s all along but they were much less at each bm in quantity and size. I stopped the meds because they made me feel worse. I went to see a gastroenterologist for which I am scheduled for colonoscopy/endoscopy in 1 month. The last few days, the original symptoms have returned, noisy stomach sounds, gassiness at times, explosive air, stringy tiny pieces of stool. I ve been tested for food allergies which I was told could cause these symptoms but all were negative. I wonder if there s a test that I should be doing, stool samples or such, which I could do to find out if I actually have an illness that can be treated. I am a female, 50 yrs, and take Levothroxine for hypothyroidism, and Lexapro, occasionally for anxiety/sleep which I sometimes alternate with Tamezepam.