LOST 100GMS

Weighed in tonight and lost 100grams ....still have 500gms gained last week to get back to where i was....why is it i gain then lose when I'm exercising 2 hours a day eating my amount of points 18 saving the bonus ones drinking my water.......making healthy choices other people have lost doing all that and not had a gain this happened once before and i chucked it in after a while of frustration not going to this time I'm going to battle this one out to the end if it kills me.....got on the boards tonight didn't have much to say though....hope I'm out of this mood tomorrow..... i think i need a day out or a night cheers