My grandson is displaying these symptoms: Nausea, vomiting, lethargic at times,loss of weight and coordination?

We tested his blood sugars twice and they were 162 &150, we made an appt. with a diabetes nurse, do you think we are on the right track. He had an Upper GI done and that looked normal, the dizziness and loss of coordination are really concerning me. Is there something else we should have checked?