<div class="accordionContent">
    <ul class="sub-menu1"><?php
        $y = date( 'Y' ); // The current year.

        while ( $y > 2000 ) { // Pick a reasonable year you want this loop to end at, to save your server some time.
            $m = 12; // For December
            while ( $m > 0 ) {
                $args = array(
                    'posts_per_page' => -1,
                    'cat'        => 7,
                    'year'       => $y,
                    'monthnum'   => $m
                );

                $cat_q = new WP_Query( $args );
                if ( $cat_q->have_posts() ) {
                    //echo $m; // This will only echo the month number, but you can figure out how to substitute it for the month's name, I'm sure.
                    $p = 0;
                    while ( $cat_q->have_posts() ) {
                        $cat_q->the_post();
                        $p++;
                    }
                    ?>
                    <li>
                        <a href="<?php bloginfo( 'url' ); ?>/YOUR-PAGE-SLUG/?month=<?php echo $m; ?>&year=<?php echo $y; ?>&cat=7"><?php echo $m.$y.'('.$p.')'; ?></a>
                    </li>
                    <?php
                }
                wp_reset_query();
                $m--;
            }
            $y--;
        }
        ?>
    </ul>
</div>