If oral intake is less,motions will not form properly,just ensure a healthy balanced diet,including high fiber items. Most fevers in children are viral in origin and take  3-7 days to subside completely. Use paracetamol for fever and repeat every 4 hours if required. If not improving OR accompanied by other symptoms like vomiting or loose motions or coughing and breathlessness or dullness and refusal to feed,consult your paediatrician asap.