Bad Sushi will do it for me!! So will a big argument with the MIL!!
Actually, since I'm mostly eating rice, my stomach pains are few, yet if I have too much fat from meats, or even curry (for curry and rice), I'll pay dearly later!! Also, it is a known fact (I read it somewhere) that potatoes and beans will cause the most gas. Ya know...beans, beans, good for your heart...!
My wife's aunt gave us a ton of potatoes, and I made mashed potatoes last night, but woke up this morning with gas pains in the large intestine (along the rib cage!), and figured it was because I ate more than my fill, and due to the stress of arguing with the MIL earlier that day! Had a long, drawn out argument with the MIL sometime after breakfast and had lost my appetite to eat anything until evening.
Which does come to another point in regards to stomach aches...changing your eating habits will have an effect on your stomach is my belief. For example, for years while living in the states, I'd eat in the middle of the night, but that would cause stomach problems during the day. Also, after developing an eating pattern in Japan, I would sometimes end up changing my eating times on the weekend, but would soon have a stomache ache by Sunday night or Monday.
My suggestion for those with frequent stomach aches that are watching <b>what</b> they eat, try for a week to make a routine as to <b>what times</b> you eat, and see how that goes. I'm kind of curious as to whether that is something for everyone, or if it will also have diffrent results.