I started having this about a month ago. During my hour long car ride to work, it felt like there was a dagger in my back (on the right next to my spine, about half way up). I was then in pain all day and my car ride home was excruciating and by the time I got home I could barely make dinner and do the dishes. Once Christmas break came, I was able to stay home for 2 weeks and I was fine. Now that I'm back at work, I can feel a dull pain, but nothing like before. I don't feel it when I'm on my couch, so I'm convinced its from the hard seat in my car with the combination of my ribs spreading to accomodate my organs shifting from my growing LO.
This, except it is on my left side. And it is always much worse when I'm in the car. I've actually started putting my purse in between my back and the seat. It forces me to sit with better posture and takes some of the pressure off of my back. I think I'm gonna buy a pillow, or something to help out.