too much uterus?

Theresa 🌙 • Hippy dippy mama. 😌
2nd pregnancy 
28 weeks along. 
1st baby was 8#5oz 
He's 2. 
The last week, baby's movement have seriously decreased. I went in today, and dr did a ultrasound to check baby. He was kicking , flipping and punching and I never felt it. I asked why, and he said from being pregnant with my son, that my son had stretched my uterus out. So basically I've got more uterus then baby. 
Anyone ever have this "issue?" I'm just wondering what exactly it means. I've got another scan next week so I'll know more then. 
From what google says, 
It means carry lower,feel movement earlier, causes more back pain along with more round ligament pains. All of which describe me to a T!