Again Steff, there are guidelines, i think that you should not exercise if above 13 as your levels can go up, and you should not exercise below 4 as you would be hypo.
Again, as Shiv said, this is what I personally do, if i was below 4 I would treat the hypo then exercise, taking on glucose (I drink the isotonic drinks, the amount depends on the amount of exercise intensity and length of time, you will get used to what you need by experimenting)
If 13 i would still exercise but not take on glucose, the exercise would bring my levels down pretty quickly (again this is just me, i know people whos levels increase with exercise at that level),
If above 13 i would take some insulin then exercise when my level falls below 13,
I know you dont take insulin but the best way forward would be to test before, during ( i test during if longer than 30 mins) and after exercise, you will see what that particular amount of exercise does to your level and can adjust amount of glucose etc if necessary.
It sounds pretty complicated but you will get used to whats right for you, the key is testing.
I drink isotonic drinks as although they are carbs they empty out of the stomach slowly and keep my levels fairly steady, most times I can remain at around 5 or 6 right the way through. Unlike lucozade for example which will shoot your level up too quickly, great for hypo but not exercise.
Not advice Steff, just my own experience, you will find whats right, but hope this helps.