Hi 
Gone thru your query regarding somach pain gas and 
diarrhea It is a matter of concern .
 Dear Cause of these problems must be your  irregular life style , eating fast ,processed foods  constantly or skipping meals  ,use of alcohol , 
smoking lack of exercise and proper sleep .
Remove the causes . Take balanced diet having all essental nutrients , fiber ,fruit,veges  lot of water .and proper exercise 
yoga ,pranayam -deep breathing  , as you are young lad  ,run a few kms to energise your self ,sleep well 
Avoid mental tention ,worry,anger, alcohol ,smoking and 
constipation  .
 Do 
meditation ,Be positive , and do your duty , whatever you are doing , do sincerely
In present situation  take lemon juice  in  a glass of warm water and a little of salt and black pepper , in sips ,It will be digested and give you relief from gas and pain . 
After half an hour again take  water same wat and add a spoon of honey in this 
.Take 1/2 spoon of bishop's seeds and a pinch of salt and black pepper with warm water , twice a day when you feel stomach pain , gas etc;
Take some 
liquid diet  , porriage  veges soups etc  , when you feel hugery  .  It will be ok 1-2 days  After that you take nomal meals other than fast foods .
If your problem  persists immidiately consult a  doctor 
Hope this helps you solve your query  Take care .All the best 
Don't hesitate to get back if have any other query 
Eat orange  apple pears , little at a time .