Hi welcome to H.C.M.Forum. in all the tests it became negative. so there is a chance for it to be allergy
some sorts of foods. possible foods are milk ,milk products, alcohol , foods stored in plastic bottels.
you are the better judge observe when you are getting , after taking what foods you are getting it.
foods irritant to your gastric mucosa
like spices chillies, some sort of foods like fish , sea foods.
eat more of curd with food. wishing for an early recovery.