Suggest Treatment For Low Grade Fever In A Child

This is in reference to an almost 19 month old female. My daughter presents this evening with temperature of 99.7 which I know is very low grade. She woke from her afternoon nap very clingy, whiny, and crying but consolable. She now cries when you abduct her right arm. She does not have strength in it and is unable to raise her hand to her mouth. She can move her wrist joint without complaint. She also did not sleep on it improperly. What could possibly be the problem? We are contemplating taking her into the ER for xrays. I have administered 5mL of Motrin for pain approximately 25 minutes ago.