How do women stay active throughout pregnancy

Mary
I'm almost 30 weeks and I'm always exhausted. It's a struggle for me to do anything. I'm not even big. I only gained 14lbs so far and I still feel like this. Props to the women who stay active throughout their entire pregnancy because I can't do it. It's really hard to find the strength to do anything these days. After work I just wanna be a couch potato and it's so bad. I have walk for about 20 mins each day and that's the most activity i do and only because it's forced. Lol no other way to get to work after I get off the train than to walk