There are many causes of "severe back pain", the most
commonCommon cold originating in the nerves, bones, joints and muscles. For example, the severe pain from a collapsed vertebra. But, the association with deep breaths also strongly suggests that it could also be pleurisy. You need to see your doctor who should take a careful history, examine your back and lungs and may want to take an X-ray.
I had the exact same problem about 10 years ago. I finally
gave up and went to the emergency room. Come to find out
I had pneumonia. I was shocked. At least get the x-ray to
possibly rule out pmeumonia.
If you have got a large amount of mucus, and because the other symptons are hard to distinguish, i would recommend that you consult your nearest doctor, and tell him how you feel.
Richard