Hi Stuart,
Yes there things you can do yo deal with the pain and that is to deal with the causes.
But before that, you should go and see your GP and get your back checked out because there are other things that can cause upper back pain not related to lifestyle.
However, from what you've said, it sounds like that the primary cause is bad posture while you're using you computer. If you work in an office then it's your employers legal responsibility to ensure your working environment enables you to adopt a good posture. But if you work from home, then it's up to you. This leaflet discusses the health problems with working with computers:
http://www.hse.gov.uk/pubns/indg36.pdf
This section of the HSE website is specifically about workplace back pain:
http://www.hse.gov.uk/msd/backpain/index.htm
You also need to look at your stress levels, too many workers seem to accept workplace stress as part of modern living, but the problem is that living with stress stores up problems for the future. Not only does it cause anxiety leading to panic attacks, but it also damages the immune system and therefore increasing your risk to cancers and heat disease. You can find more information about stress here:
http://www.hse.gov.uk/stress/
You really need to deal with these issues now before they take over your life. The good news is that they are well documented and there is a lot of pressure on employers to improve working conditions in these areas.
Remember prevention is always better than cure.
Myarka.