Doing great and then up 3 pounds!

khk2010

Anyone else have this happen? I've been really really good for 4 weeks. Stayed to my calories, making great food choices and eating very healthy. I had lost weight but then I was up over 3 pounds this week end. The only thing different is that this week that I added in exercise. I had an injury so hadn't been exercising before. I'm taking a slow 20 minute walk and about 45 minutes of light weights and easy toning exercises. What gives?