Work and Pain

I have an office job and sit at a desk all day long. I have a very cushioned chair but it does not keep the back pain away. I walk around every 30 minutes or so, but as soon as I sit back down, the pain comes back. My baby girl has gotten to where she likes to rest in my ribs (that or she's sitting on a nerve) and it makes the pain even worse. Any advice on how to help with the pain?