C-sections

So I had my first c-section back in august it was an emergency c-section and I’m pregnant now again and due date is estimated around mid November … they say to wait 18 months apart from having another baby if you want to deliver naturally . The doctor told me if it’s under 18 months I’ll have to have a c-section every time if I don’t wait …. Is this true? And for anyone that’s had a second c-section does it hurt more because you’ve already had one ? Thanks