Having chronic back pain for more than 6 months definitely needs concern. At this point it is not advisable to try different medicines instead it's very important to evaluate the root of pain and treat specifically. If after osteopath the pain is not relieved then it is advisable to take an X-ray of spine initially, if that is not confirmatory of the cause then an MRI scan of the back is essential.
I would suggest you to take an appointment with a GP as early possible. After evaluating you thoroughly with few blood tests if it is general soft tissue injury he might be able to treat by himself with a stronger Analgesic and Anti-inflammatory medicine along with physiotherapy or if GP suspects degenerative disc disease and other orthopaedic problem he might ask you to consult an orthopedician.
Meanwhile, try to be on rest as much possible, take precaution to not to strain your back by sitting for long hours or lifting heavy weight. If you are running frequently you are supposed to change your shoes about every 3 months.
Back pain can be a precursor to symptoms like numbness or weakness that extends down your leg. This is because the repetitive running motion can cause a disc to slip out of place, which places strain on the nerves that run down your back. So without any delay, consult a GP and seek for a definitive diagnosis.
Hope this helps. Please feel free to ask if you need further help.