The human body is susceptible to a range of illnesses and diseases which can be diagnosed through the various symptoms that they themselves with. There are some symptoms that are common across a range of illnesses.
The symptoms that you have mentioned are loss of appetite and fever. These could be caused by a simple case of the flu or by something that could be far more complicated. Because the appetite is affected, the problem may be related to an issue in your digestive system like a stomach infection. It could also be unrelated to the stomach as a loss of appetite could be a result of general malaise. Fever occurs when the body begins to fight an infection or illness. For your symptoms you should try simple home remedies for a day or two. If there is no improvement in your condition, you should visit your doctor immediately for testing and diagnosis.
The first simple thing to do is to take some paracetamol tablet. Paracetamol is recommended as a general medication for a common cold or flu like symptoms. During your illness, be sure to hydrate yourself more than you normally would. Because your body is running a temperature, you will require more liquids to help your body cool itself down. Electrolyte drinks are recommended in this situation as they provide an extra kick to the body to help it fight the fever.
For the other symptom that you have mentioned, a loss of appetite, try and eat smaller meals more often. Three meals a day could be split into six snacks a day. Keep the food fresh and light, but do not have any junk food at this time. Your snack should simply be a smaller quantity of your normal meal. This would help you gain the same amount of nutrition as you would normally do and also accommodate your loss of appetite. You can try and eat lighter food and avoid extremely fatty or heavy foods that are difficult to digest.
If you have abdominal pain as one of your symptoms, the matter becomes more serious. This could indicate an infection in the abdominal area. The abdomen contains several organs such as the kidneys, stomach, intestines, appendix, and so on. Appendicitis could be another cause of your trouble.
Because you are running a fever, you should take rest and not stress yourself or your body. A cool shower is recommended if your temperature is constantly high.