Pregnancy weight gain help!

Kayleigh
I am 27+1 today and a first time mom! I had my glucose test this morning as well as my normal 4 week appointment. I have gained 10 pounds since my last appointment which concerned me. My weight gain was fairly slow at the beginning having only been about 5-7 pounds up until my last appointment where I shot up 6 pounds in a month, and now this appointment was 10 pounds!!! I started weighing 149 and now weigh 172 😰. He said I'm measuring about 28-29 weeks but all looks good. He isn't too concerned about my weight gain but to just keep an eye on it. I'm just at a loss for what to do and how to manage it so I'm not just packing on the pounds. My diet hasn't changed since I've been pregnant. I eat a bowl of dry cereal at 8:00 am, granola bar at 10:00 am, low calorie yogurt, a banana, and granola at 12:00 pm for lunch, a snack of a fruit or skinny pop popcorn at 3:00 pm, and then dinner with my boyfriend around 5:00-6:00 pm. Sometimes I'll have a small snack at night after dinner but not always. I walk 8,000-10,000 steps a day and go up 15-20 flights of stairs a day all according to my Fitbit. I'm just confused why I'm packing on so much weight and if anyone had any tips! Sorry for the long post!