What Causes Recurring Bouts Of Vertigo?

My 10 year old grandson has been having bouts of vertigo, sometimes with a headache, and occasionally some nausea. HE has had an MRI which showed nothing out of the ordinary, he has had an echocardiogram which again showed nothing out of the ordinary. These bouts of vertigo are occuring more frequently, almost like in clusters. He has an appt with an ENT in March, but until then, he is experiencing these symptoms.