Have you spent ages looking through Facebook to find that post you liked?
Go into your activity log, and it will show you everything you have commented on, liked or posted.
On a PC it is the small arrow in the top right:
Locate the button in the top right corner of Facebook. Select Activity Log.
Mobile or Tablet
On a phone it will look like this:
Select the icon in the top right.
Select VIEW PROFILE, then Activity Log.