Since 4 years ago in left midback i get occasional tingling that comes and goes. it often goes away after 1 or 2 massages and may come back after months. last 2 weeks it happens on the other side of my back. my upper back is stiff from poor posture?

While this could be an aggravated intercostal nerve, the fact that it is intermittent and goes away with massage suggest that this is likely a partial charley horse (myofascial nodule) in the latissimus dorsi muscle caused by exceeding the endurance capability of the muscle through pulling or pushing down. Cardio/endurance exercise can usually decrease the frequency of attacks.