Loose Weight Before Graduation

Hi, im a senior this year and will be graduating in may. I weigh about 150 and want to get to at least 120 so i feel healthy and right about my weight for once. Yesterday i bought a pilates video and started using it and am watching my diet and drinking either tea or water. And im also doing a mile on the treadmill at least once a day. What else can i do and how long do you think it will take to shed the weight?