What Causes Severe Pain In Lower Back While Sitting?

My back started hurting a few days ago around the middle somewhat towards the bottom. I haven't lifted any5hing I have actually been out of work and it has gotten worse over the past few days I am going to see a doctor tuesday but ibuprofen isn't doing anything. It hurts to stand up straight the only sort of relief which isn't really any is when I bend over. If I sit in a chair or lay down it hurts worse. What is happening