You have a pinched muscle some where and I don't care how long you do that arm band thing, it isn't going to release the muscle giving you the pain. Here is how you can release your back muscles:
Back:
Place your left hand on your left leg and try to keep it straight. Place your right hand over your left shoulder and with your fingertips find the muscle next to your spine. Press on it and hold. Relax, take a deep breath and exhale and don’t tense up any part of your body. After about 30 seconds there should be a release happening and when it does slowly lower yourself forward onto your right leg. If you can lean over the outside edge of your leg it will be better for your release. Continue holding for a total of one minute. Then release but rest your body there for one minute longer. Then reverse and do the right side.
Then place the hand of the arm that hurts on your lap next to your body and keep it stiff so your shoulder is higher than normal. With your other hand reach over the shoulder and press into the back of the shoulder where the muscles are that are hurting. Press into them with your fingertips and hold. Now relax your whole body, take a deep breath and exhale and don't tense up any part of your body. After 45 seconds, slowly remove your hand that is the prop and lift that hand to shoulder level and across the front of your body as far as you can. Release the pressure but hold your arm there for another 30 seconds.