One week in - gained a lb.

Hello Fellow MFP friends! I was on a weight loss plan counting points for about a year and a half, and was successful with the plan up until recently. My body hit a plateau at around 160lbs and for ten months I titrated back and forth five pounds. I stopped my point plan, and a week ago joined MFP. I work out at least 3-5 days a week (circuit training, running, walking) and am alloted 1200 calories. Every day but one I stuck to the 1200 calories intake (regardless of exercise). One day I did have a bad day and went over about 700 calories. I started last Tuesday, but wanted to weight myself Monday mornings - and it says i'm up a pound. Not sure if this is normal, or if I need to adjust something? I would like to lose about 25 additional pounds to get in my healthy weight range (i'm 5'4"). Any suggestions would be helpful.

Thank you in advance!