Okay so the past few days I've been having pain in my middle back, like the back of my ribs, when…

Okay so the past few days I've been having pain in my middle back, like the back of my ribs, when I'm sitting down. I know it's probably because baby girl loves to be up in my ribs... I've been applying heat but it's getting to the point where I pretty much can't sit down without a heating pad on my back... Any thoughts on a way to relieve this pain?