I am not sure if you are asking about what to eat when you have a common illness
(such as a cold) or if you mean that the fact that you frequently do not eat because you are on the go gives you an unpleasant feeling in the stomach.
In the case of the former, the best rule while suffering with a common illness is to drink plenty of fluids. The body needs fluids more than food when it is sick. It is also best to avoid dehydrating beverages (such as alcohol and caffeine) while ill, focusing instead on water, juice, and the like. Simple, bland foods such as crackers, fruits, and thin soups are often easier to digest, especially if you have nausea. Stay away from spicy or greasy foods.
On the other hand, in the case of being constantly on the go, forgetting to eat will lead to a sour tasting stomach and perhaps nausea. You might be able to avoid this by making sure to pack your bag when you leave in the morning with small snacks. This way, even if you do not have time to stop and eat a full meal, you will at least have some nutrition throughout the day.
Feel free to talk to your primary care doctor
at any point about how to keep your nutrition up and how to deal with the stress of being a college student.