How can I lose 20lbs FAST?

I'm 5'3 and 150. I have been exercising ALOT... walking at least 2 miles m-f and playing basketball m-th. I do not look FAT just thick, but I don't like the way I look AT ALL! I usted to weigh 120 2 years ago and I want to get back there. I need to loose weight fast(within 2 months) but I don't want to put the weight back on. So what can i do? also would it be safe to just get my "energy" from diet fruit drinks for a few weeks? suggestions... please!