How can I lose weight quickly and effectively?!

I've gained weight since I was in high school (I'm almost 21) and I'm really sick of it. I'm 5'6" and 109 lbs, I used to weigh 102 lbs for forever and I like how my body looked then better. Whenever I've tried dieting I usually wind up hardly eating two or three days then eating too much junk and it's just cycle. Has any one done something that's been really effective? I don't have allot of time to work out, I'm in college full time and working.