Why can't anyone tell me what is wrong with her?

This same thing happened last year. Katy is always sick. Last year she was sick from December to April and it looks like she is having a repeat. She has been sick so much and none of her medical staff knows why. She will be fine and then an hour later she is running a 104 degree fever. An hour after that she is fine again. She coughs all the time and sometimes so hard she throws up. She also gets slow gastric emptying, meaning that her stomach slows way down and it takes forever to digest. I change her diet to help and it usually does improve, but then it comes back. I am never going to get her to gain any weight at this rate. She will gain 2 or 3 pounds, then go through one of her spells and lose it all. She just can't break the 25lbs mark. I just want to know why she keeps getting sick. I can't keep dealing with this all the time, I am already the busiest mommy in America, I don't need even more to deal with.