Melting the kg's

I don't get it. At the start of the week my weight had gone up to almost 75kg. I was delighted to see all my hard work and persistence paying off with my weight coming down a little each day. Last night I weighed in at 72kg. This morning after a 30min workout and before eating I weighed in at 73.4kg. That does not make sense at all. I don't get it. I am not going to get disheartened though. I week of dieting and exercise is not a true indicator of how this is going to work out. All the same, I want to be close to 70kg within 2-3 weeks to be on track to reach 65kg by Christmas.