As it is there seems to be a claim that the RAM isn't all seen. You mention the last time you checked there was 6 GB or RAM; but what do you have if you check now?
Have you looked in Task Manager to see if anything is spiking up and staying at 100% usage? I'm thinking CPU and/or disc usage.
CPU spike makes some sense. So it doesn't look like any particular process which is keeping the laptop busy and thus slowing it down. Which leaves the question of what's happened to the RAM.
Next question: is this 6GB of RAM installed when buying the laptop or upgraded to it later? (It's an odd RAM amount.) It does start to look like a need to open up the laptop to reseat the RAM.