Fatigue After Bowel Movements. Have Acid Reflux. Did Vaginal Ultrasound, Colonoscopy, Ct Scan. Tests Negative. Suggestions?

Hi! My mom has been having really bad fatigue/weakness after her bowel movements. She says she has a bowel movement four times in a row and then she gets hit with severe fatigue and weakness, all she can do is lay down. She's also complained about acid reflux some in the last few days. The weakness and fatigue has been going on since April of this year but seems to have gotten worse through the summer. She has been to countless doctors and they all tell her she's healthy. She's been to the E.R. and had her blood work done (twice), the test come back clean. She's had a vaginal ultrasound, abdominal MRI, colonoscopy, xrays of her abdomen, an EKG, and a CT scan of her sinuses/brain. Every test is coming back negative but she is still feeling horrible. Can you offer any advice as to what it could be or any guidance to other tests that might need to be run?