Weight gain

So I had my monthly appointment. I was already feeling pretty bad about my weight gain, then my dr reminds me that I've gained 20lbs so far. I'm 25 weeks, which is considered my 6th month. She makes a comment that I should get out and walk more. I told her I work as a sales manager and I literally walk all day long. 8-10 hours a day, with 1 hour for lunch weekdays, and only 30 minutes on weekends. I don't get to sit down. I don't get weekends off. I'm lucky to have my two days off together. I'm just really frustrated. I eat 3 meals a day.