Hi,
Welcome to Healthcaremagic
Thanks for your query
The cause of a pain varies with nature of work, age e.t.c. Middle back pain can be related to strain which could be due to prolonged sternuous posture, or some anatomical problem like scoliosis and kyphosis, or else due to disases like tuberculosis of spine. Please get examined by orthopedician.
Take care

Hello
Thanks for nice query.     
Middle back can be due variety of reasons ,simple pain due to muscle spasm or due to some organic cause .So get the x-ray spine done to find the cause & consult orthosurgeon .
‘Hope I have answered your query, I will be available to answer your follow up queries, “Wish you Good Health and trouble free speedy recovery”

pain has a definite pathology,so in aggrement with both the doctors who have answered earlier i must add that no over the counter drug or massage or any physical modality like heat should be strictly avoided except in expert guidence as they may subside the real clinical picture and may pose later serious hazards,only thing you can do to get relif before you approacch an expert is
LIE ON FLAT BED WITH NO PILLOWS,YOUR POSTURE SHOULD BE SUPINE I.E LIE ON YOUR BACK YOU CAN USE ROLLED TOWELS UNDER YOUR BODY COUNTOURS.
STRICTLY AVOID ANY EXERCISES OR STREACHING.

hello jess:
Dr.alok sir an Dr.savita mam is right you follow dis suggestion and treatment. one thing i tell you.that you should to do assessment on your work station..it'll better to identified the actual causes of pain.. this assessment done by occupational therapist.