You can't insert a section break in a text box, only in the main text layer.
To see what is on or just before that blank page, start by showing invisibles. Click on that last blank page & press Delete (the one on the main section of the keyboard), perhaps more than once, & see if that extra page disappears.
My guess is that your text boxes have wrap turned on & they are "pushing" any returns or breaks to cause a new page. New objects of any kind, including text boxes, have wrap turned on with a 12-point gutter/extra space. Unfortunately, there is no way to set this to not be on when objects are inserted.
