Medicine is not an exact science -
yet. The reason being is because we humans are not exact duplicates. We have unique chemistry, DNA ,etc. Scientists have high hopes that in the next 50 years a patients medicine will be tailored exactly for them, everything from diagnosis to treatment will be tailored to fit the patient.
How medicine is performed is to gather a list of symptoms, and based on those symptoms come up with a short list of most likely ailments that fit the symptoms. Tests are performed to either confirm a a diagnosis or to rule out potential ailments if the list is to complex.
For your age and depending on the location, an infected appendix would be the most likely cause. EXAMPLE: Appendix, kidney stones, endometriosis*, ovarian cysts (among others) can have the same symptoms. Since you are young and I assume not sexually active, the most logical and common ailment to diagnose would be an appendicitis (infected appendix).
The Doctors went with the most common potential ailment (Appendicitis), and did imaging to confirm the diagnosis. This is exactly as it should be. used to be, before reliable imaging techniques the doctor would diagnoses appendicitis and the patient would be operated on (opened up) to have a look see if the appendix really was infected. More often than not to 'justify' the procedure (even if no infection was found) the appendix was removed.
Trust me, you do not want to have things removed for no reason... even with a good reason being sliced open can be miserable.
As for the oral dye they used, you need to memorize the exact name and make certain you list it as one of your allergies each time you visit a doctor.
The most common dye they use contains Iodine. If you have an allergy to the dye it is most likely the iodine.
http://www.livestrong.com/article/275077...ng-iodine/ Is a list of foods that contain iodine. Most people who are allergic to shellfish are actually allergic to the iodine. Most who discover they have an allergic first have a rash, later on down the road if they continue to eat shellfish (high levels of iodine) they end up with anaphylaxis =
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001847/
It is important to know this and to be wary. Anaphylaxis can be deadly.
So you need to find out what the contrast dye contains and potentially get a test for specific chemicals (such as iodine if it used it) to see how allergic you are so you can regulate your diet and keep the allergy from getting the best of you.
*
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001913/