Fever, Vomiting, Diarrhoea, Tylenol, Stomach Virus. Diet And Treatment?

My 21 month old daughter has had recurrent high temperatures for the last 6 weeks up to 104F and comes down with Tylenol and remains low grade most of the time. It spikes usually once or twice a day. She also has massive diarrhea that is watery and green (sometimes greenish yellow) also for the same 6 weeks at least once a day up to 4 or 5 times. She got sick while on a trip between NY and Germany (I think from a 2 hour gym daycare) and the first week was persistent fever , vomitting, and diarrhea. I could barely get her to keep anything down, but her appetite seemed ok, she was irritable but not lethargic, not losing too much weight, but I was up almost every night and all day long changing diapers, sheets, clothing , sometimes changing 12 watery stools a day and little urine which caused diaper rash . I took her a doctor after about 2 1/2 weeks of this and he suggested a liquid only diet for 3 days, which I helped but the diarrhea and vomitting began again as soon as the diet ended. I stopped giving her fruit juice and she doesn t have dairy as she s lactose intolerant, that helps but symptoms still continue. A few days ago I left her in the care of a friend when her fever spiked to 105 and caused her to take her to the emergency room and another doctor visit 2 days after. Every doctor has said she has a stomach virus, but why would it last so long? None of the doctors have even suggested any testing be done either.