What's wrong with my daughter?

I recently took my 3 year old daughter to DIsney World in Orlando, & she's been weird ever since. She began coughing on the plane ride home, & I figured it was just a random cough. It didn't stop though, so I took her to the doctor, & he said it was nothing. She's had a fever of 99-102 for a few days; nothing brings it down. I've taken her to different places to get her checked out, & nobody is doing anything to help at all. I've found nothing online, & this is really a last resort. I'm so worried, I know it isn't whooping cough because they did a test for it & she's been vaccinated. please help? :\