Why is my phone senconds behind everything I do

The main I would look into is your ram usage. Tap the lower left bottom (next to home button) to open the app manager and shut off all the apps. If its not the left button hold down the home button to display app manager and shut everything off..

Go to Settings > Apps > Select/Swipe to the Running Apps.

On the bottom of your screen you will see the ram usage. Most units, based of those I've worked on, run smoother when 25%-40% of the ram is consumed by the operating system. If the usages is going above 60%-70% after you shut off all the apps, this usually indicated that you may have some other things running.

You can do a trial and error and start removing unusual apps, or you can take the quick approach and do a factory reset and update the unit to most current OS.

Hope this helps, if not let me know what you have noticed. Good Luck.