Fact is, you may never truly understand what causes your upset stomach problems.
One reason this may take so long to figure out is that you may be eating (or drinking) multiple things that cause your stomach to experience different levels of stomach queasiness. Another reason is that you will sometimes experience a queasy stomach when you are sick. This is more likely when you are suffering something viral.
Your body also may react to different foods than others. You might not be able to eat those spicy foods like some of your friends. You may have to learn this the hard way. A good example is Ben Stillar when he ate spicy foods in the movie Along Came Polly. That was a funny movie no doubt but a lot of people suffer from IBS (Irritable Bowel Syndrome) as Ben did in the movie. It leaves them running to the bathroom as shown in this clip:
I too suffered from IBS. In fact, if I did not have an upset stomach, I would be surprised. This is because I was in a constant state of irritated bowels.
It took me years to really figure out what was consistently causing me to experience queasy stomach symptoms. I knew I would suffer stomach irritation if I ate things like salad, broccoli, corn, okra and fried foods (these are just of few of the things that would upset my stomach). It took medical problems (chest pains) to get me to start eating better. After about a month, I could tell my stomach problems were almost completely gone.
Another month, and it was smooth sailing.
I was 44 years old before I figured out how to eliminate my queasy stomach. It took God slapping me upside the head and waking me up to discover this. The one thing I figured out was that it was not just one thing that caused my queasiness, bloating, and diarrhea but it was really a mixture. I could not eat all of those tasty foods I mentioned previously because I was eating poorly constantly and putting my stomach in constant distress.
When I had no choice but to eat properly, all of this changed.
I realized I could eat things like broccoli, salad and corn as well as okra because my stomach was not irritated anymore. It now had been restored to what seemed like a natural state in my younger days.
If it was not for this wake up call, I would still be eating complete crap food and gaining weight and suffering from IBS and a queasy stomach.
Things are different now. I eat a much healthier diet, I exercise regularly and go running on a consistent basis. My cholesterol has dropped along with my blood pressure. I feel so much better and the best thing of all is that I do not have to go looking for the nearest bathroom shortly after I have eaten.
You may never figure out what causes your stomach problems or it may take years to figure it out. My suggestion (and it is only a suggestion) is to cut out nasty foods like fast food or fried foods. Completely remove unhealthy foods and eat a strict diet for over a month and see if that does not make a difference. Chances are that if you follow these suggestions, you are more likely to eliminate your queasy stomach symptoms that are caused by food. If you have severe stomach issues, please make sure you consult a physician.