Hey,

Just a few hours ago, I was sitting down, and I felt fine, then when I got up, I had a pain in the area circled in the picture. I've had little minor pains before, and they usually just go away. So I went to the gym. I did one set of deadlifts, and I had to stop. It really hurts right now, but I can't seem to find the muscle that hurts. No matter where I press I can't get any indication of pain. It only seems like when I move my left shoulder that it hurts. Does anyone have an idea as to what I did?I generally don't sit with very good posture, but this has never happened before.

Well that could describe several things. I've had my back get really unhappy and painful from sitting awkwardly. It's hard to say whether it's a muscle or a nerve. You could always try heat, ice, rest, and an anti-inflammatory for a few days.

These things are most commonly (IMO) caused by postural imbalances. I have random spouts of back pain from time to time and saw a posture specialist. I have an elevation and twisting of the pelvis and rounded shoulders (as do most people) which causes certain muscles on one side to compensate for weaker ones. This pulls your body out of alignment and you get pain and/or injuries. I've been told weight lifting reinforces those imbalances so it's best to get your body into a more functional state before heavy strength training.

This information may or may not apply to you, but I've found that nearly all people (especially those with desk jobs or repeptitive movement) have an imbalance that needs correcting. It's akin to driving your car when the wheels aren't balanced properly. You can drive it for a while but eventually you'll blow a tire.