Didja swim in the lake?
If so, you may have giardia. Not good.
Otherwise, it's probably rotavirus. We picked that up on our last trip to Disney, despite using gallons of hand sanitizer, and my 5 year old puked the whole 8 hours home, then I puked for the next two days.
The absolute best anti-nausea medicine, bar none, is Zofran.
You will kiss the ground I walk upon and thank the gods you discovered this drug (used for chemo patients, mostly, to help with nausea) because it's SOOOOOO much better than fenergen.
The good doctors at Celebration hospital gave it to me the FIRST time I picked up a stomach bug at Disney, about 4 years ago.