Upper left to mid left back pain when i breathe in deep. it's not an excruciating pain. today makes the 2nd day of the pain. a bit worried. any ideas?

Pleuritis?: Pain with breathing as you describe makes me wonder if there is inflammation in the lining of the lungs. There are musculo-skeletal explanations that need to be ruled out as well, even shingles could present like this. If the cause is not obvious a chest x-ray could be helpful. These symptoms do warrant a visit to your doctor.