Don't stress out about a new back pain. Lower back pain is very common, especially among middle-aged Americans. It is unlikely to be an indicator of a more serious disease or condition, and it will likely clear up over time even if it is not treated by a medical professional.
Don't ignore the pain. If you know a particular activity is going to exacerbate your pain, then don't do that activity. Ignoring it will not make it go away faster. In fact, pushing through the pain will probably result in further injury, making the pain last even longer.
Consider switching your most commonly used chair into an ergonomic chair. There are several ergonomically designed chairs these days that are made just for those that are sitting at a desk or sitting up all day. These chairs promote better positioning within the chair, thus offering a greater amount of comfort and less stress on your back.