At your age you must be T1 (I think) as far as I know it is pretty much only carbs that send T2 high.
Carbs send BS up and insulin brings BS down. I am sure there are other factors but that is the most important thing to remember.
So my guess is you have been messing with your routine and/or the carbs that you eat,
You probably know, but for completeness, the major carbs are anything associated with grain or starch (potato) and all forms of sugar including fruit and dried fruit particularly grapes.
At your age, I expect that your Doc would not want you deviating too far from a recognised balanced diet so your routine is important so it can be matched with your insulin dosing. You might find you have to vary your insulin with activity changes like sport.
So the way to go is take lots of tests and then identify and remove the spikes.
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