I have been carrying my Glock 19 in a Galco King Tuk holster, which overall I really like. It conceals very well for me under just a t-shirt and is really comfortable for sitting on soft surfaces like a couch. The only issue I was having is some lower back pain after carrying it all day. I have chronic issues with my lower back that I can usually keep in check with stretching and exercise, but carrying the gun was really bothering it.
Today I decided to try out a little theory. I have a double magazine pouch that I use for IDPA, and I figured I would try to carry that on the opposite side of my gun and see if that balanced me out. Not to get into too much physiology (I am a science person by profession), but we are designed with what is called axial symmetry. Meaning that our bodies are symmetrical on either side (at least externally). Having the weight of the gun on only one side was causing an imbalance and therefore some pain in my lower back.
Today I carried two full magazines and was much more comfortable than usual. It is 9 o'clock here and I have no pain at all. This also helped in the car because I carry my Glock 19 at about 5 o'clock and the magazines at about 7 o'clock, so they provided equal support while sitting. Before carrying the magazines I would lean to my left while sitting and wearing only the gun.
I know this is not overly scientific, but I figured I would post it and see if anyone else has had a similar experience, or this may give an idea to someone who is experiencing discomfort with their current carry set up.