Macbook Pro 9,2 SSD unstable (constant loading)

Background information:

I am using a Macbook Pro 13 in (Mid 2012 version)

Using Samsung 840 evo SSD for over a year

Latest version of OS X Yosemite

Problem:

The SSD has worked fine for over a year now, then all of a sudden Yosemite started showing a circle with slash at startup but it would still start up and work fine. Then out of nowhere my mac became very unstable taking 10-20 seconds to do anything (constant beachball loading).

Attempt to fix:

I have used disk utility and smartmontools and both show that the Samsung SSD is healthy.

To determine if the SSD was the issue I swapped the mac SSD with another Samsung 840 evo that I had on my windows machine but that was not the problem because my mac is still the same and my windows machine is still just as fast.

Then to determine if SATA was the issue, I swapped my Samsung 840 EVO for the hard drive that came with the macbook pro, but the hard drive works fine and is way faster than the SSD.

I don't know what else to do, any suggestions?