I Hurt My Lower Left Side Of My Back The

I hurt my lower left side of my back the week before Thanksgiving with taking care of my dad who was on hospice. I did all the things I was supposted to do and I thought I was all healed up? Well one week ago I tweaked it again in the same place and so Im wondering how long does a lower back injury take to heal? Im using ice, taking ibuprofen and taking it easy. Im still working 8 hours a day "sitting" at a desk which I think is part of the problem? I do walk at breaks and before work on the treadmill. When I wake in the mornings I have little to no pain and then as the day goes on Im in a lot of pain. How long does it usually take to heal?