What could be wrong with an 11 year-old that has a headache a fever and dizziness?
An infection could be the cause of those symptoms. If the child is extremely dizzy and feels that either she/he is spinning or the room around her/him is spinning, should could have a condition called Vertigo which can be caused by a middle ear infection. Although not life threatening, if your child also complains of a stiff neck, please visit a physicial IMMEDIATELY for she/he may have something called Meningitis (inflammation of the membranes surrounding the brain and spinal cord) which can be fatal withing 24 hours if left untreated.
"Cold sores", also known as "fever blisters", are caused by the herpes simplex virus. Symptoms include, (but not limited to) cheek/gum mucosa inflammation, headache, nausea, dizziness, fever, sore throat, dysphagia (difficulty swallowing), lymphadenopathy (swollen lymph nodes). So to sum this all up yes you can get sick from a cold sore.