I have a really bad pain in my back!!?

I think its the way I sit at my computer but lately for the past 2 days, when I have sat at the computer I get a really bad pain on one side of my back. When I bend forward it hurts even more, and yesterday when I was cooking I had to bend over to get the ingredients and utensils and i felt sick. Whats wrong with my back and how can i fix it?