Problem in Macbook Pro Hard Disk .

I have a Macbook Pro (13-inch , Mid 2012) with 4gb of ram and a 500gb Hard Disk .

Recently , My mac became very slow , the beach ball shows up every couple of seconds .

I went to my Apple Retailer and he said that you have problem in your hard disk . He changed my mac harddisk and it went blazing fast . I came to my home without buying it . I used Disk Utility to find errors but it does not show up any errors in my harddisk.

I made a clean install of Yosemite with bootable usb , thinking that this would done the trick . But it failed . IT TOOK 2 DAYS TO install Yosemite on my mac.

and my mac was very slow again .

My mac has almost 470 gb free storage .

Can I do something to fix it without changing my hard disk ?