If your fasting reads are 7 mmol/L or under you are likely not diabetic, as that is within the normal range, albeit at the high end. That could be a natural place for you, or it could be a sign of things rising.
As a blood glucose reading is just one moment in time it is not enough on its own from which to make a diagnosis, but it is a sign which can suggest further action such be taken, such as an HbA1c. But it sounds like that is already the case, with your doctor monitoring you for prediabetes, and you are taking monitoring your levels and diet.
As for morning levels being higher, the body does a lot of things overnight, different hormones are released to work whilst you sleep. Some of these have the effect of increasing the release of glucose whilst inhibiting the effects of insulin. This causes levels to gradually rise, but in a normal healthy body this is detected before waking and insulin released to compensate. However in diabetics, and regardless of type, this compensation may not happen which is what causes increased levels when waking. But precisely why this occurs, despite good control and taking medication or insulin, is not known.
Although a waking level of 7.2 mmol/L is outside the normal range, it is only slightly over and the margin of error for a glucometer of 15% means it could actually be as low as 6.1. Again it is only something I would worry about if it is a trending upwards or your normal fasting level, rather than treating readings as absolutes where 7.0 is still good (being in the normal range) but 7.1 is suddenly bad (being above it).
