What Causes Appetite Loss With Loose Motions And Constipation?

Three days ago my daughter began showing a decreased appetite and has had loose stools and constipation. Last night she had a low grade temp of 100.5 and vomited. She isn't complaining about being in pain but has said her stomach hurts from time to time. I'm wondering if I need to call her pediatrician or if it could be viral and will run it's course. Also, she has urinated once in the last 13 hours - the majority of those hours were over night - she is 3 and potty trained - when she woke up last night vomiting, she did not have to go the the bathroom.