Hello, i work as a water delivery man. So i always carry water gallons and water cartons. Recently, i am getting skinny and loss weight.. So how gain weight by eating food that doesn't make me stomachaches and diarrhea?
Last time i eat goreng pisang, i get diarrhea. I eat spicy food like ayam goreng McD spicy, i get stomachaches..
I need advice for eat or drinking for gain weight but don't cause my stomach in pain?

Eat high protein food like mushroom, chicken breast etc. If can't eat spicy food, dun eat them.

Speaking of stomach ache, are you lactose intolerant? Dairy stuff like milk, cheese and yogurt will cause stomach ache and diarrhea.

try to build muscle

But i always drink coffee and tea using diary creamer, will that also give stomach pain?

Creamer is not really dairy stuff. One way to test is avoid dairy stuff for a week, see if you still get diarrhea or stomach ache. Be sure to avoid spicy and chilli stuff just to be sure.
The other way, the bad test, is to skip breakfast so your stomach is empty, drink a couple glass of fresh milk at lunch and see if you get diarrhea within several hours (usually two hours).
You can also confirm it by clinical tests.

coffee promotes bladder, it's normal. if severe pain maybe you have weak stomach wall

TS sounds like he has frequent diarrhea and stomach ache. I would say maybe he/she has some sort of allergy or intolerance. Of course they could be many reason, and bad diet habit also needs to be factored in.

Considering most Malaysians are actually lactose intolerant with varying degree of tolerance level, TS may have low level tolerance.

The first step though is to identify the cause of diarrhea and stomach ache. A simple step is to reduce your diet to the safest one, no milk, no caffeine, tea or coffee, no gluten, and such. I don't really know the exact steps and all, but I know that's one of the thing you need to look at.

That seems serious, maybe he need full body checkup