I would imagine that you are retaining some water from your new exercise routine. Every time I changed or added things to my exercise routine I retained water - sometimes as much as 6 pounds.
I found that I didn't lose every week. I kept a spreadsheet with my weekly weights and my average loss was around 1.8 pounds per week. Some weeks zero, some weeks 3-4, some weeks gained. If you are doing everything right with the food and the exercise don't worry so much - give it a couple of weeks and I imagine you will lose again.
It will settle back out. Just keep on track.