Weight gain?

I’m freaking out cause at 27 weeks I’ve already put on 18 pounds!!! I gained 45 with my son and he was 10 lbs 11 oz!! I’m so scared my daughter will be huge too!! I gained 8 in the past 4 weeks!! Doctor is talking c-section which is my biggest fear... I managed to push my son out vaginally with no issues but what if she’s bigger? I indulge in my cravings but I wouldn’t say I eat junk food ALL the time. I have tried exercising but I have SPD so I end up feeling like I got hit by a truck by nighttime. I honestly don’t know what to do to slow down my weight gain. I was about 160 to start so I wasn’t exactly small to begin with! Someone please calm my nerves. Maybe you can give me advice? I don’t have gestational diabetes so it’s not that..