jQUERY: Interval doubles?

doing a bit of jquery to make an image rotator, Got it rotating nicely, however i am now trying to make previous and next buttons. I have encountered an issue, the next button works but doubles the speed of the interval despite clearing the interval?

Any ideas?

   $(".hero").first().addClass("active");
   var rotate = function () {
       setInterval(function () {
           $(".active").next().addClass("active");
           $(".active").prev().removeClass("active");
           if ($(".active").next().length < 1) {
               $(".hero").first().addClass("active");
               $(".hero").last().removeClass("active");
           };
       }, 5000);
   };

   window.clearInterval(rotate);
   window.setInterval(rotate);

   if ($(".hero").length > 1) {
       $(".hero").append('<div class="previousArrow">prev</div>');
       $(".hero").append('<div class="nextArrow">next</div>');
       $(".nextArrow").click(function () {
           window.clearInterval(rotate);
           window.setInterval(rotate);
           $(".active").next().addClass("active");
           $(".active").prev().removeClass("active");
       });
   }