Hi isk.
Yet again, a GP who is talking rubbish. If he is any good he should know what are the advisable levels. They are certainly not 12 - 13. Has he /she taken out a Life Insurance policy on you ?
Can you see another GP in your practice, someone who knows about Diabetes.
I do not know what Carobo food is ..? However most breads, cereals, pasta, rice, potato and starchy root veg will possibly elevate your Bg levels. The only way of knowing is to test 2 hrs after your meals.
As stated before your diet is the first thing to try then if that doesn't work possibly some medication.