Possible JRA in my almost 4 year old???

Last week we flew from Chicago to Aruba. After the first day my son had what we thought was sun poisoning with fever and rash. He spiked a 103 fever and then the next day felt great. Fever free he went down to the pool and enjoyed his day, but night he had a fever and more rash. By the 4th day of our trip my son had fever, HUGE hives (pink patches the size of my palm) on his upper legs, stomach, back and his knees and ankes were swollen and his was in so much pain that when I "made" him stand to show me he puked. He is 3 1/2 I have NEVER seen anything like this. We took him right to the emergency room where they called it an allergic reaction. The next morning he woke and after awhile could walk and seemed fine, then again that night everything flared up in his knees and ankles again and he couldn't walk, just a little rash this time. He has NO known allergies or other health problems.In the past he has complained in the morning or after activity that his legs hurt, he won't walk down the stairs on his own some mornings crying that he can't do it. We always just thought he was faking it. Doctors are trying to tell us it is viral, but it was all too strange. The weather change was dramatic and I have a slight form of arthritis from 3 knee surgeries and it acted up badly while in Aruba. Does anyone out there have a similar story where thier child ended up with Juvenile Rheumatoid Arthritis?? My doctor doesn't sound convinced, but I am worried. THANKS!