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I would immediately get a worming tablet and see the doctor this sounds like a worm or parasite issue. Simple but don't leave it too long depending on what the parasite is.
Get a prebiotic capsule and take them in the evening for a while and see how that goes, if nothing else works. I would go to the doctor though first. Tropical countries are notorious for nasty tummy bugs.
Go hard on some metamucil for a week or so.... i recently did after never doing it b4 lost 1.5kg !!! Make of that what you will hahah