Your all problems is due to your digestive system. Your food in not digesting properly and hence you are not gaining weight. The Nausea
and disturbed bowels movements are due to:
1. GERD: To get rid form this try to be standing position for at least 30 minutes after every meals. Do not lie down after meal.
2. Inflammation in GI track: Endoscopy
is the diagnostic procedure for this and accordingly antibiotic, antacids and PPI inhibitirs can be taken.
Disorders: Do your Liver function test and avoid fatty, oily and spicy food.
Try to take high fiber diet and plenty of water. Do regular exercise and avoid stress
Consult your Treating doctor and go for required investigations. Hope this will help you.