We Have Been On Vacation Walking Around Washington DC For

We have been on vacation walking around Washington DC for four days. My 7yr old daughter who is athletic and usually full of energy has been slightly lethargic. Sunday night she vomitted everything in her stomach after dinner. Her doctor said there was a 12-24 bug going around. She has seemed fine except she has an aching pain at the bottom of the left side of her rib cage. It only bothers her when she walks quickly. She has not eaten very much, but she is not a big eater. She just woke up at 3am (two days later) and vomitted again. She said she felt better and just went back to sleep. What are the possibilities?