Unwanted page breaks during OTD to MOBI conversion

When I convert my OTD file to a MOBI file, Calibre automatically inserts a page break on every new header 1 and 2. My problem is that my book is structured somewhat like this

1. Chapter 1
   1. Chapter 1.1
   2. Chapter 1.2
   3. ...
2. Chapter 2
   1. Chapter 2.1
   2. Chapter 2.2
   3. ...
3. Chapter 3
   1. Chapter 3.1
   2. Chapter 3.2
   3. ...
4. ...

The title of x is always on a its own page with the title of x.1 and its content being on the next page.
I want there to be a page break at the start of a new chapter and a new subchapter, except x.1, without removing x.1 from the index.
How do I accomplish that?