Weight loss isn't linear. You don't lose the same every week, and absolutely it's normal to experience a week or a few of not losing at all.
You just started exercising more. That often leads to water weight increase, which masks fat loss by taking up the 'scale' value to hide it.
Stay the course. Stick with it.
Your BMR is NOT any indication of what you should eat. There are some "they" who say "never eat below your BMR". However, I've also heard "they" say "if you want to lose weight, just eat under your BMR". So which "they" do we listen to?
Here is how Spark calculates your range, perhaps this will help explain how BMR factors in, but is not the absolute value itself: www.sparkpeople.com/resource/calorie_calcu