Leveling out

I began my fitness journey on January 4th, 2010, and my first month was sweet. I dropped 9 lbs. Since then I've only dropped 8 more and its been almost double the time. I update my goal every so often to bring my calories to where they should be, but it seems I'm starting to plateau. I'm still losing, but not as fast as I need to. I have 10 weeks to lose 19.5 lbs. My goal was originally on my birthday of May 18th, to weigh 175, but my cousin is really trying to lose too, so we set a bet for June 1st. But now, its like I'm barely losing. I know that I have the weight to lose, its not like I'm just trying to get toned up, I'm definatly on the big girl side, but what can I do to help me lose a little faster. I work out 5 - 6 days a week, on my cardio only days I do 45 minutes to an hour, and on days I do my strength training, I do 20 to 30 of cardio and 20 - 30 strength training. I eat my add'l calories, try to mix in lots of fruits and veggies, and I always get my 8 glasses of water. Any suggestions would help a lot! Thanks.