Hello..... the most common causes of back pain arise mostly because of bad posture or abnormal posture..... I need to know what sort of work you do so that I can relate it.... I suggest you to take hot bag and keep on the area of pain for temporary relief....if there is sudden increase in weight then that might also be a reason  for it....stress will not be reason of backache.... thank you ....consult an orthopaedician...