Onglyza seems to work in the same way as Januvia (sitagliptiin) as far as I can see. It is not an insulin stimulating medication and works by suppressing the take up of glucose. Many people who take the more well known Januvia say it works well but like all diabetic drugs isn't a magic bullet. My own opinion is no diabetic drug apart from maybe a move to insulin works anything like as good as sorting out your underlying diet. I simply take Metformin and maintain non diabetic blood glucose levels (between 4 & 6) 98% of the time by simply adopting a low carbohydrate diet. That means I've given up anything with sugar in it apart from a small amount of fruit and importantly I have drastically reduced the amounts of starchy carbohydrates I eat so that's rice, pasta, bread, cereals, potatoes and any other things made with flour. I've replaced with extra meat, cheese, eggs and vegetables. Using this diet I went from an HbA1c of 11.3% to 5.3% in just 4 months and at the same time lost 3 stone in weight, normalised my cholesterol levels and my blood pressure. I now feel the best I have done in years. I saw my gp last week and my DSN the week before and both have told me to continue doing exactly what I have been doing as it obviously works really well. It's not magic its just what you would be recommended to do if you where lucky enough to live in more enlightenned countries such as Sweden, Germany and America where this kind of low carbohydrate diet is recommended for T2 diabetics.
Most members would recommend you test your own blood sugar levels. Has your doctor ever given you a meter and strips? Some do and some don't. It's a bit of a post code lottery and we've found some progressive surgeries are pro testing and others anti. I'll warn you the anti ones can sometimes be very vocally anti! Mine was anti until I showed them how much it was helping me and now they are prescribing me strips. Before the change of heart I funded my own meter and strips like many forum members end up doing. As a long term diabetic you probably know the reason testing is important as you should try and keep your blood sugars below 8ish two hours after eating any meal. Above the 8 value is where the dangers of complications do begin to occur according to diabetic experts.
Here's two good links about what's good to eat.
First is the lady doctor who's low carb / low GI recommendations seem to form the basis of what's recommended in Sweden
http://blogg.passagen.se/dahlqvistannika/?anchor=my_lowcarb_dietary_programe_in
Second is a good beginners guide to low carb regimes that are excellent for reducing blood sugar levels and losing weight.
http://www.dietdoctor.com/lchf
Hope that helps