I just keep gaining weight! why?

I mean i was eating really badly at one point but then i stopped, and for a couple of weeks i've really cut down my intake, on weighed myself last saturday and today and i've gained 7lb, how is this remotely possible, i haven't eaten more than 2000 calories for a week, and these past 2 days i haven't eaten more than 1,000! i'm crying, which is soo pathetic, but i used to be 9 stone and pretty, now i'm 11stone and it just doesn't look right on me!