This is Dr. David
with dieting and weight loss if you are eating less carbs, you most likely are having excessive stomach acid production
your stomach is used to you eating more carbs and calories
and when you eat less of those, the stomach acid can inflame the stomach and cause gastritis and pain in the upper abdomen
excessive stomach acid can cause more gas and burping as well.
stomach acid blockers like zantac and prilosec can help decrease stomach acid.
also excessive fatty foods from meats can inflame the gall bladder.
you need to cut down on your fatty foods and alcohol to decrease gall bladder inflammation
you should see a doctor or go to the ER
where they can check a gall bladder ultrasound to check for inflammation
and also they can do blood test for amylase and lipase to check for pancreatitis inflammation
pancreatitis inflammation can cause pain radiating to your back
let me know if you have questions.