Can be a lack of stomach acid, ironically. It can be that plus an infection, such as h pylori, can be a histamine response as well.
The best way to start is with a digestive enzyme- a gentle middle of the road enzyme called digestzymes by designs for health, comes to mind. If you do not find relief with this- you can take 2 caps of olive leaf extract and then follow with digestzymes (best taken with meals)
I tried to answer your question and would like to get your feedback for possible continuation of our conversation, but I don’t get it, why?
I would suggest eating less tonifying foods such as meat and dairy because they will make the pain you feel in your stomach worse. Only eat these foods in the morning and never past lunch time.
A piece of fruit will highly reduce burning in the stomach but only temporarily.
A nutritionist would be highly beneficial in your case because you need to figure out how much protein you require and only consume it in the morning. If you eat it late at night it wont get digested quick enough to be properly evacuated from the stomach. If you sleep and food sits in your stomach you will wake up to processing over digested food and that is toxic to your body, especially your stomach.
Hope that helps a little bit and inspires you to see a nutritionist.