Well Im a veggie and if you take a look at the numbers on the left you'll see that you certainly can lose weight on SW.
I think the questions the others have raised are key.
Firstly what have your losses been? Are the really slow or is it just that your expectations are too high?
Secondly what are you eating? Are your meals based around carbs or fruit/vegetables? I have carbs at pretty much every meal, although I do not have the same one more than once a day. However my meals are packed with veggies - think along the lines of EE and made sure you have a minimum one third superfree foods as this helps with the carb portion control. I also have wholegrain versions of carbs rather than white as these are more filling - you eat less and they keep you satisfied for longer.
Look at introducing more of the other green foods into your meals instead of relying on pasta, rice and potatoes - what about lentils, pulses, quorn or other meat substitutes, cous cous, quinoa and bulgher wheat?