passing ‘&’ in return function of add_filter

First thing is you are returning jQuery through PHP without script tag, so you should at the least be using this:

add_filter('the_content', 'my_drama_func'); 
function my_drama_func () {
    return "<script>function getthrough() {
        jQuery.ajax({
            url: 'ajax/ajax.php',
            type: 'POST',
            data: 'url="+url+"&un=0&pretty=1&mega=0&click=true',
            beforeSend: function(b) {..snip..},
            error: function(e) {},
            success: function(s) {}
        });
    }</script>";
}

I hope you understand by using the filter on the_content and not returning the original content, you are making it so any post will not show the actual content anymore, only your jQuery. If you just want the jQuery appended to the content you should at least append jQuery to original content:

add_filter('the_content', 'my_drama_func'); 
function my_drama_func ( $content ) {
    $append_jquery = "<script>function getthrough() {
        jQuery.ajax({
            url: 'ajax/ajax.php',
            type: 'POST',
            data: 'url="+url+"&un=0&pretty=1&mega=0&click=true',
            beforeSend: function(b) {..snip..},
            error: function(e) {},
            success: function(s) {}
        });
    }</script>";

    return $content . $append_jquery;
}

You can also use PHP to output the url string like so:

add_filter('the_content', 'my_drama_func'); 
function my_drama_func ( $content ) {
    $url_args = "&un=0&pretty=1&mega=0&click=true";
    $append_jquery = "<script>function getthrough() {
        jQuery.ajax({
            url: 'ajax/ajax.php',
            type: 'POST',
            data: 'url="+url+"" . $url_args . "',
            beforeSend: function(b) {..snip..},
            error: function(e) {},
            success: function(s) {}
        });
    }</script>";

    return $content . $append_jquery;
}

But this is just a fix I can give based on the limited details you have provided. What are you actually trying to do? This may (and probably isn’t) the right way to do this, but it should work