Pain on upper left side - liver?

Hi all!

For the last 3 days I have been having a dull ache that comes and goes on my upper left side - right under my ribcage. Could it be liver pain? When I press it, I feel something move there. I wasn't sure if it was my intestines or liver. I looked at a diagram of the body and it seemed that the liver went all the way across with the largest part being on the right and a slimmer part of it being on the left.

Thanks!