My 3 yr old has had a fever for 4 days?

Any fever over 3 days is dangerous,it is exhausting so much that the immunology system can't fight sufficiently.you should call a doctor or ambulance if fever persist, as there might be serious infection going on,and you need to lower the temperature (baby paracetamol)as well as fight the reasons not effects.to help with breathing use some eucaliptus oils and keep his head up on the pillow so he can't suffocate with nose and lungs discharge if there is any.check his tonsils, if swollen, call ambulance straight away,ask to drink lots of liquids.they should always be able to take a sample of his saliva, blood and urine tests. Its also good to order home visit.if there is any infection they should be able use antibiotics and other medicines.