The likelihood is that you are running high blood glucose levels and as Rosiecarmel says, that can cause frequent urination. In order to get things under control you need more information though. When you test, do you test before and after meals or just at particular times?
I think, to give yourself a shock, you should test before eating anything you shouldn't (but I'd rather say "not to excess") and then test 1, 2 and perhaps 3 hours after. That will tell you how your body can cope. The possibility is that you will be going mid to high teens (and perhaps even higher). If that is the case then you need to cut down on that carb or stop it altogether.
If things don't improve, though, go and see you Gp. Don't just let things roll on. Also, bear in mind that it may have nothing to do with your BG levels.