As Sue said, portion size is important. From what I have learned, so is your eating schedule.
Since I lowered my carb intake I don't get hungry in the same way, I was almost always hungry before. Now this is great in terms of weight management, but, I'm now realising, not so good in managing my BS levels. My blood sugar during the day can go quite high from liver dumps if I don't eat, so I have found that I need to organise snacks as well as lunch. Add to the the liver dump the effect of eating whatever I have prepared for my lunch or snacks and I'm sometimes going unaccepatbly high - I may go well over 8 sometimes, if I have not been able to get something to eat.
You might need to tweek your meal schedule as your testing regime gives you more information about what is going on with your BS. Also, eat to your meter as far as you can. If your BS is high to start with, have fewer carbs. Not always easy if you have a packed lunch on you.
there was a very interesting program on the TV a month or so back about diets and exercise. Amy Lame (and several other celebrities) was in it and she was exploring exactly how little exercise you can do to keep yourself mobile and buring off the energy - things like taking the stairs rather than the lift and getting off the bus a bit earlier and the calories burned doing housework... it was very good and I have adopted some more of these techniques. Moving around seems a lot easier when I'm not carrying so much weight. But overall the impact of excersise is small on weight loss.
Exercise is good for you, it does burn off glucose because aerobic/cardiovascular exercise wakes up the insulin receptors. However, turing fat in to muscle is a bit overrated interms of weight control, as muscle weighs more than fat. I am adopting mostly the Amy Lame approach at the moment, having fallen off the regular cardivascular workout wagon a few weeks ago. However, I have noticed improvements in my body shape and I can see muscles these days
I have had some of my lowest readings after a cardiovascular workout on my exercise bike, but also some unexpected readings too, although I think the unexpected readings may be due to fluctuating hormones. Do something and test