I've Been Crying

So, over the last year and a half, I have managed to put on 20 pounds. I am currently depressed about this. I mean, very very depressed. It seems no matter how much I try to watch what I eat... Let me put it another way. I constantly feel like I am starving. Not just hungry, but starving. I feel like if I don't eat I will die. I have always had issues with my weight, but nothing so severe as this. I don't know if it is because of my age. I don't know if there is something medically wrong with me, but something has got to give, and fast.
I have been trying to do more exercise, and maybe I have been trying to push myself too hard to fast. Maybe that is my current problem.
Oh, I also quit smoking. It has been... 2 weeks? Maybe 3... I haven't really been keeping track. That won't help me counter the weight gain, or the extreme depression that seems to be coming with it. I have to do something about this. I can't go on being so downright sad. I'm sure it will eventually put a strain on my relationship with my wonderful boyfriend. I don't want that to happen.