You can't spot reduce, so there's no point in trying to selectively lose weight off your stomach. Your body will get rid of excess fat in whatever order it wants to.
I would just try a different kind of exercise, swimming or cycling, for example. The reason is, once you've been doing something for a while, your body becomes more efficient at it and manages to use a lot less energy (not very helpful for those of us trying to lose weight). By doing something new, you will make your body work hard again while it gets used to the different form of exercise.