Brief Answer:
most likely its irritable bowel.

Detailed Answer:
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Have gone through all your details most likely possible cause for all his symptoms is irritable bowel.
Irritable Bowel Syndrome (IBS) is a diagnosis of exclusion where symptoms include chronic abdominal pain, discomfort, bloating, and alteration of bowel habits etc.Its not necessary that every patient has all symptoms. IBS patients usually experience frequent change in bowel movement patterns, frequent occurrences of diarrhoea accompanied by tenesmus (a constant urge to evacuate the bowels after eating food).

Suggestions-
Ash him to
-Start taking a probiotic(VSL#3) twice daily,Probiotics contains lactobacillus. These are good bacteria's help in proper digestion of food and will help to revive your depleted gastric flora.Gut flora is the complex community of microorganisms that live in the digestive tracts of humans. The intestinal microflora is a complex ecosystem containing over 400 bacterial species. Probiotic mechanisms of action include enhancement of the epithelial barrier, increased adhesion to intestinal mucosa, and concomitant inhibition of pathogen adhesion production of anti-microorganism substances and modulation of the immune system.In LAY MANS language it contain a lot of bacteria's which forms a part of normal gut flora,Hence it substitutes the flora lost during a pathological condition and improve digestion.In the same way Prebiotics are undigestible food ingredients that beneficially affect the host by selectively stimulating the growth of a limited number of bacteria in the colon, thus improving digestion.Again the work is same to stimulate the growth of the bacteria's in gut flora.Hence overall both of them help restoring the lost gut flora and helps in digestion. They are definitely very good for patients with irritable bowel syndrome in long runs.
Take Fybogel husk-Fybogel sachets and Fybogel Hi-Fibre or Metamucil sachets both contain the active ingredient ispaghula husk.It will improve your bowel habits.It will help forming bulky stools.Initially soak it for 20 minutes in XXXXXXX warm water after that take it.
Give him external enzymes to increase appetite.
Therapy with Ciprofloxacin and metronidazole can be given initially for 5 to 7 days to rule out possibility of chronic enteritis.


typically, food that is ingested in someone with enteritis or ibs is still digested appropriately and absorbed into the intestines, so malabsorption is not a common mechanism of weight loss in these cases. One exception to this is in pernicious anemia, in which vitamin B12 is not absorbed properly, which can lead to anemia and fatigue.
On a more serious note, unexplained weight loss is always a worrisome symptom, and an underlying cancer is something that always needs to be ruled out. If you have had an upper endoscopy performed as part of the evaluation of your gastritis, then the stomach lining has been visualized and presumably no sign of malignancy was detected. However, if you have not had this procedure done, then it is something to consider in the appropriate clinical setting. It is advised that you speak to your primary care doctor about your weight loss so that further work-up can be done as indicated.
Start following the advices if weight gain does not occur in a month then malignancy has to be ruled out.

Regards.

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