You can't assume that a 14 year old girl has the same nutrition requirements as a grown man. To put it plainly, it's not only what you eat, it is more whether your body can process it. Your system isn't designed for elaborate meals. Your stomach acidity adjusts to what you are eating. If you eat a lot of carbs with your proteins then the stomach contents may exit before the protein has the ability to be properly digested. This causes problems in your intestines. Your body is a machine and like any machine, if you don't know what you are doing then you can damage it. Stomach pain is more likely the result of digestive issues, from poor food combining or eating more food than your system can handle. If you really want answers about what you should be doing then you need to keep track over time and use the process of elimination. You need to consider what you ate, when you ate, what you did, how much you slept, what time of month it is (girls), and the consistency of your feces. Your stool will tell you more about the effectiveness of your diet than Google. Our systems are similar but all slightly different. What works for me may not work for you. It has to do with our digestive enzymes, and how effective they are at breaking down the food we eat so our systems can extract the nutrients. Some people may benefit from apple cider vinegar to increase gut flora, or eating vitamin C with their protein to help dissolve it into amino acids for the body to use. If you want advice about vegetarian diets I think JosephsDreams is the voice you should heed the most.