BuddyPress.org

Fixed it by changing it to this:

function bp_template_content_sub_function() {
    if ( is_user_logged_in() ) {
        //Add shortcode to display content in sub tab
		if ( bp_loggedin_user_domain() . '/mystocks/activity/' )
		{
		echo do_shortcode('[user-activity]');}
    } else {
        wp_login_form( array( 'echo' => true ) );
    }
}