How do I get a section break/page break when the item is greyed out?

Question

I've created an A4 document in word processing mode, with four identical A6 text boxes covering the entire page. Then I've created a second page with four more A6 text boxes so I can print a postcard on both sides of the card. Trouble is, Pages has made two extra text pages that I don't want, the first is linked to Pages 1 and 2, and the second is separate. I can't create a section break or page break because the command is greyed out, so I can't delete page 3. When I try and delete page 4, which is a stand alone page, it also deletes pages 2,3 and 4, leaving me with just page 1!
I don't have any problem with page breaks or section breaks in an ordinary A4 document with just one text box on a page, but I often want to create multiple text boxes and when I do I have always had this problem, ever since Pages was first introduced. Can anyone tell me what I'm doing wrong, please?

Answer 1

Thank you, Yvan, but I've tried that. Firstly, I unchecked the headers and footers tick box in the Inspector because I want the postcards to be exactly A6 size, that is, one quarter of A4. I've tried making the lower two text boxes slightly smaller (which I don't really want to do, because I want them A6 size) but I still can't get the insertion point to appear below the text box – it stays resolutely in the next page and won't go back up to the previous page. Any further ideas? Thank you.