Overcoming Dietary Challenges

My wife got pregnant a little over 2 years ago with our first kid. In her third trimester, she started experiencing digestive issues that caused her to lose so much weight that her body is forcing itself to shut down. This issue seems unrelated to her diet, eating habits, or ingredient intake, and it is not consistent. After a second pregnancy, it got worse, and the medical system cannot figure out what is going on. Now she is 28 years old, has had 2 kids within 3 years, and weighs 92 lbs. She feels weak and tired and can barely function as a mom most of the time. I would really love your input on this situation.