13 month old vomiting? Should I be worried?

Each of these symptoms alone is fine. However if a fever takes more than 2 days to break, they need help. Not to bring the fever down ( treating the symptom) but to help them get rid of whatever the actual problem is. Fevers exist to kill off viruses and infections. They are neccissary to get better, however, when they are coupled with lythargy like you are describing theres cause for concern. If she isn't holding down enough water, she will get dehydrated very quickly. I am very hesitant to medicate my children and really believe their bodies can fight off most things. But, there are times when you need the help of a good doctor and this sounds like one of them. Especially since you still are unsure of the cause. I hope she feels better soon.