Q: MEMORY FULL macbook pro 2012

Hi , Can any one help me with my macbook pro memory.

At first i noticed that my 4GB memory was almost full and Photoshop and Safari items  started to jump around or took a long time to do there operation.

So i purchased 8 GB, this was fine for about a week, Giving me 4.5 gb of spare memory.

Now the problems have started again, telling me only 1 GB of memory spare.

Even if i turn off and restart it goes straight back to 1GB running space .

I have tried with no Apps running, just finder running, still the same .

Checked activity monitor and it is full of items, that i have know idea what they are.

Is it possible to clear memory and start a fresh.

Thanks Bob