31 weeks 4 days dilated & bed rest

Tuesday we went to the doctor and I was 2 cm dilated and my doctor placed me on bed rest with having 3 other kids total bed rest is kind of impossible. We were told he was developing macrosomia at 20 weeks and I’m not an overweight lady . Which means large bodied baby. All my other kids were 9&10 lbs. I’m wondering if that is what’s causing dilation so fast? Pre term labor was stopped at 24 & 28 weeks. How long did you guys stay at a 2 before labor? And I have no mucus plug anymore and she said when she checked me she could feel his head 😳 any advice would be awesome!!!