Try stretching exercises that are held for a few seconds at a time, such as Yoga poses. Also try topical ointments such as BenBay or moist heat such as a hot shower or hot tub.
Stand upright, arms down at sides, then push your shoulders towards your back and hold for 5 seconds,repeating at least 5 times. Stand erect, hands on hips, bend over backwards.
IF you have experienced pain for more than a week I would see a doctor. However, gentle excercise could help if the knot is caused by stress or tension. However, do not do anything that could causes severe pain as you could injure yourself further.
there are many exercises one such exercise is first lie down on your stomach hold your foot with your hands and pull yourself backward. try to sit or stand straight so that your back doesn't pain much. bending exercise forward and backward may help you. if this doesn't work see a orthopaedic.