Stress and anxiety are also one reason of stomach upset. AFAIK, gambling is all about stress and anxiety. I remember when I use to gamble I have sleepless night and day was full of anxiety. I tried medication but nothing went my way. I got rid of these problems only when I left gambling. Now I just read stories about how people are losing money and getting problems with gambling.
For this it is always better to have a healthy life, that is, to eat well, preferably with fruits and also to play sports, sports make the physical changes much better and that those twists of stomach pain or something like that do not come back, also It is necessary that from time to time some vitamins are taken.