What Causes Persistent Fever, Vomiting, Headache With Neck Stiffness?

My son had been vomiting from wed. To Thursday night...he had a fever about 38...he seemed to have had recovered he complained about a headache today and a stiff neck...since he is on the autism spectrum a clear straight answer is hard to get by... now the fever is back only a bit higher...could it be something serious such as meningitis?