hi as you mentioned your problem it appears to me that the lung is not getting properly ventilated due to which the oxygen carrying blood to the brain is on a lower side which is also asking to yawn more and demand of the oxygen by the brain and body is getting fullfilled by this way. Also the muscles of the back are getting physiological barrier due to the less oxygen levels. I will recommend you to do some breathing exercises, like - deep breathing, costal breathing, pursed lip breathing, diaphragmatic breathing and abdominal breathing. Focussing on improving the ventilation capacity of the lungs will help the lung tissue stronger. Also perfroming abdominal strengthening exercises will provide an additional assistance to the respiratory system as well as the spine. By which the pain in the back will come down and the functionality will improve. Also doing simple sit to stand exercises for a repetition of 50-100 in breaks will help improve the Cardiorespiratory endurance and the breathing capacity will also improve. I wish you a speedy recovery. regards Jay Indravadan Patel