Why is my job causing weight gain?

Before I started working, I was very inactive. I pretty much laid around in my bed on my laptop most of the day. I started a job at Target about a month ago and I work around 25-30 hours a week. I'm on my feet lifting and bending all day. Before this job, I had stayed around 100 pounds for the past 3 or so years. I noticed I started slowly rising when I started working. I just weighed myself today, I'm currently at 107. What is going on? I guess I do eat more since I started, but I'm also a lot more active. Can anyone explain this?
Why is my job causing weight gain?
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