The back pain is due to continued sitting for prolonged duration. Try to take few breaks during your travel and walk down a little. If your job requires to sit then that adds to the misery. For your height the bike may be low as well which will add to the postural issues. Take breaks and do the stretches for spine and lower limbs.

Need more information Any pain going down to leg, any numbness in foot, any fever ,any swelling How intense is pain etc