Bummed

Yesterday was weigh in day. I have been so good with my eating. I eat sensibly. I eat very few carbs, I exercise... I passed on cakes on Monday at school. It was chocolate day and we, the teachers, were the judges. Didn't try one although the chocolate smell chased me all day. There was cake for snack on Friday. I never went near it. I haven't had fast food since January, when I started trying to control my eating... well... and the reading on the scales yesterday was +700gr (about 1 1/2lbs), WTH???? I was upset, of course! What am I doing wrong? I've only just started, it CAN'T be a plateau, can it???
So, a 9lbs loss for a total, when last week I was at 11lbs lost... oh well... time to stick to it and keep going. Hopefully the weight will end up coming off!!!!