Hi Marina! I am a volunteer with Medhelp and the Juvenile Diabetes Research Foundation (JDRF) and the mom of a 17 year old who was diagnosed at the age of 21 months. I am not a medical professional, so please verify any information with your healthcare team.
High bg readings in the morning can be caused by a couple of different things. The first one being, not enough insulin. This can be caused by not injecting enough insulin at bedtime (not all the insulin was injected - bubble? or poor injection site) or by hormonal changes (in adolescents, the growth hormone works it's hardest at night, making insulin less effective). Contacting your endocrinologist and discussing dose changes would be recommended at this point. The other reason for high AM bg's could be a bottoming out during the night. If the bg goes too low, the body's own defense system may kick into effect and the liver produces glucose to protect the body from going any lower. A good way to verify which one of these possible reasons for high AM bg's would be to do a 3AM bg check. This should give you a big clue as to why the morning bg is too high.
I'm also not a physician, but a longtime diabetic.
To amplify a bit of GGs answer, many diabetics experience a "dawn phenomenon" which is managed automatically in non-diabetics. As a normal part of our physiological preparation for the day, hormones are released in the early morning hours. Those higher levels of hormones require additional insulin to keep BGs in the target range.
This is quite common among diabetics, type 1 or 2. Type 1s can often tweak insulin -- after doing some 3am & 5am tests as GG recommends. As GG said, some mornign highs are the result of going too low during the night, and having a rebound when the liver kicks in some glucose to treat it. Only with overnight BG tests can you discover what's going on for you.
For Type 2s, having a small bedtime snack that includes complex carbos & protein can reduce the morning highs. This doesn't work for Type 1s because our bodies function differently.
Since you've noticed a pattern, now' a good time to write down details (dinner & night-time snacks, BG before bed, insulin or other meds, and overnight, early morning BGs). Armed with that info, you & your endo or CDE (certified diabetes educator) can likely figure out the root cause and a reasonable way to fix it.