<s>[INST] Hi my 3 year old daughter got her flu shot a week ago. For the past 4 days things haven t been right. She ended up with severe diarrhea 4 evenings ago than the following morning she threw up but only once. Then again diarrhea yesterday morning and this morning throwing up a few times. During this time she has had no appetite but drinking lots and even though always saying she is tired has a normal degree of energy. Today now she is complaint of sore legs especially the feet. Any ideas on what is going on? [/INST] Welcome to the ChatDoctorAn episode of acute gastroenteritis can deplete a child of vital electrolytes sometimes if not rely Chat Doctor.  This is known as electrolyte imbalance. It seems your child might be having either an electrolyte imbalance or a rare probability may be benign acute childhood myositis episode(BACK). I would suggest you to go for a proper clinical examination followed by laboratory evaluation of serum Sodium, Potassium and calcium levels. In case BACK suspected, CPK levels will be helpful. In the meantime you can give her Acetaminophen for pain relief along with oral rely </s>