I want to lose 25 pounds, help?

So I'm 5'5", and I used to weigh 140 pounds, buy sonehow over the past 2 months my weight has gone up to 155 pounds. WTF. Someone help me lose 25 pounds please. I'm a vegetarian, and reeeally picky about food. I really dont care how long it takes I just want to be thinner by Christmas. All of my clothes still fit the same as they did when I weighed 140, what does that mean?!~ My measurements are 36-28-38. Good or bad? please help!