Walked in cold weather, middle of my back became sore, and when i breathe i feel some pain in my left chest, what's wrong?

Pleuritic chest pain: The pain when you breath is a sign of irritation of the lining of the lung (pleura). This can be minor and go away without treatment or can be a sign of more serious heart or lung problems. If it is severe and/or persistent you should seek immediate medical attention in person. If it is mild and without other symptoms or underlying medical conditions you may try OTC analgesic medications

See below: Regardless of the outside temperature, by the time air reaches your lower windpipe(trachea) it is warmed to 98.6F body temperature and cells in the trachea give up water make the air 100%humidified. Air tends to be low in humidity in cold weather so the cells can become severely dehydrated when exercising in cold weather which causes chest pain on breathing. I can't account for the back pain.

Depends...: If you aren't used to exercising in cold weather, you could merely be experiencing airway irritationwith referred pain into your chest. it resolves quickly when you rest and warm up, it's not worrisome. However, the chest pain persists or worsens or you start wheezing, you should seek medical care promptly.