I've been having upper back pain on my left side, towards the middle of my back, just to the side of my ribs, that worsens during the day and is pretty unbearable by the end. I think it has to do with sitting all day. I have a maternity belt I got on Amazon, but I don't think it's the right type of support since it's placed on the lower back and my pain is localized much higher. I get some relief from pressing my upper back against the lumbar support pad I have on my desk chair, but otherwise I can't seem to escape the discomfort. I'm sure lying on my back might help, but I'm in a cubicle at work so it's just not feasible. 
I'm going to call my OB about this, and I have a massage scheduled for Saturday, but if anyone has any tips that have helped them, I'd be so grateful to hear them! 
                
December '14 November Siggy Challenge - How I Feel in Third Trimester 
Re: Upper back pain on one side
Sounds like typical "pregnancy discomfort". I'd try a chrio. Couldn't hurt to make sure everything is aligned correctly.
DS 06/2013
DD 12/2014
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D14 November Siggy Challenge: The feels of 3rd trimester...
Also, unrelated to the post, I love all of your Halloween free-for-all pictures! I need to come up with one myself.