Hello, A 10 Year Old Boy Has Been Diagnosed With

hello, a 10 year old boy has been diagnosed with UTI yesterday after having suffered from severe headaches, nausea, drowsiness and high fever for 2 days. although the fever has gone down a bit but he still feels weak and unable to stand and is still suffering from the headache and constantly vomiting whenever he consumes anything. please advise what can be the cause as his doctor is not being very helpful regretfully.