Prolonged hypoglycemic episodes

My son is a Type 1 diabetic who was diagnosed just over three years ago. Just over 2 weeks ago he started having hypos, starting around 20:00 hours lasting for 2 - 6 hours. This week his hypos have started approximately 2 -3 hours after lunch and continuing until 2 - 4 am the next day. The diabetes team suggested that he had been injecting in the same sites and this could be the cause. He has changed his injection site and he has had no change to these hypos. I can also add he had to do an experiment for them, where from the onset of his hypo, treat with lucozade (80 ml) every 10 mins until he reached over 4 m/mol then have a slow carb....... 2 ltrs of lucozade, 1ltr of coke, and starting on a bottle of shloer, we had no joy! We have stop his novorapid insulin with meals and we are now considering stopping his levemir.
The diabetic team have ruled out Addisons disease and Cushing syndrome.
Has anyone experienced anything like this before?

Thank you everyone. I have cut his basal in half and the evening hypos still happen but for a far shorter period. The diabetes team have told me not to do any more for the moment and have fitted him with a continuous blood glucose meter and monitoring him for five days so they can help us with new insulin to carb ratios. I'm keeping my fingers crossed.

Thanks everyone once again!