I would agree with both of these statements. Chronic use of pain killers can, ironically, lead to what are called rebound headaches or overmedication headaches. The treatment is weaning off the pain killers and then reassessing the situation. A neurologist experienced in managing headaches can develop a treatment plan for managing the pain while coming off the tramadol and co-dydramol.
While coindidence is certainly possible, and this would have developed anyway, it is also possible that you "triggered" the syndrome when you banged your head. In other words, you were predisposed to getting rebound headaches but they did not start until you injured your scalp and skull (where the pain fibers are) or suffered a concussion with injury to the neurons of the brain (that don't actually feel pain, ironically)...or both. It is certainly possible that these new headaches, whatever the cause (and it might be a complex interplay of forces) will subside within the expected timeframe of a concussion (3-6 months). It is also possible that your clinical situation has changed for good now. This is why working with an experience neurologist could be so important.