What Causes Belching And Nausea In A Child?

I am worried about my 5 year old daughter. She was fine all day until last night after we came one from a birthday party. She insisted on sitting in front of the toilet and said she is going to throw up. She stayed there for over an hour, and would not move. Finally I talked her into taking a bucket into our room and try to sleep. Every couple minutes she would grab the bucket and hold it under her thinking she was going to puke. She has been carrying a bucket around all day today too. I am concerned because she says her neck hurts, although she has no problem moving her neck down to her chin. She has had a rash that I thought was just chapped skin on her hands (not the palms but the tops of her hand which look like chapped skin). She has had the chapped looking skin for a couple weeks not, but now she has a rash around her her mouth that looks like dry skin too. She does not have a fever and has yet to throw up. Sometimes she does say that she feels relief from throwing up after a big burp comes up?? she also has been very lethargic and watching a movie in the dark she says it is so bright and hurst her eyes, which never bothered her before? She also has complained of a headaches. She had the flu, with lots of vomiting and diarrhea about a week ago. Do you think I need to be concerned with this or is it just another flu bug?