Hello, in my opinion these two are separate issues. It would have been helpful if you would have specified the name of antibiotic which you have been taking, since you are still getting these symptoms of chills, i advise you to visit a ENT surgeon so that you may get opinion whether you need to change your antibiotic as of now. And for the issue of Back pain, you should visit your orthopedician for the same. For the back pain, you must avoid bending and lifting heavy weights from the ground. Try applying some liniments containing capsaicin and diclofenac gel so as to reduce pain sensations and put a heat pack over the area. consult your orthopedician if in case you may need some radiological investigation like MRI or Spine X-rays. take certain mild pain killers belonging to NSAID s like ibuprofen or diclofenac and take an antacid too to avoid gastritis associated with it. you may also need an opinion of Physiotherapist.