...
my $rxHeader = qr
   {(?x)
       (?: (?<=\A) | (?<=\n) )
       ([=]{2,})
       ([ your big character class ]+)
       \1
   };
...
while ( $post->{ post_message } =~ m{$rxHeader}g )
{
    my $section =
       get_section_code( $2 ,$post->{ post_message } );
    my @subheaders;
    while ( $section =~ m{$rxHeader}g )
    {
        push @subheaders, $2;
        ...
    }
    push @headers, { Section => $section, SubLoop => \@subheaders }
}