Well, a pain management specialist might not be the best person for the job in this case. I've been to a few pain specialists and they've honestly been great but I don't think that they provide the kind of treatment that you probably need right now. In the case of physical trauma a pain specialist typically, well, works to reign in chronic pain that comes from an injury that a patient is either recovering from or cannot recover from. In short they treat the symptoms but not the cause (generally).
It's good that the sharp pain has subsided but the abscence of pain proximal to your injury doesn't necessarily mean that the injury is no longer causing problems--I'm sure you know this and I don't mean to sound patronizing but it's an important point. Your protruding disc could be pinching or damaging a nerve or blood vessel; the shift in your spinal column may have changed the pressure of your cerebral spinal fluid; the accompanying muscle tension may be triggering headaches in a variety of ways--these are just purely speculative potential sources of your headaches. Your headaches might not even have any direct connection to your displaced disc (an MRI can only show some of the very many potential headache sources).
The point that I'm driving at is that, if your back injury is under control then your main problem is headache. With that in mind it may be wise to see someone with more experience in treating headaches. In most cases of chronic headpain I recommend seeing a headache specialist--they've simply the best equipped to help you. However, in this case a general neurologist with experience in treating headaches may do just fine (particularly considering how long you sometimes have to wait to see a headache specialist).
In any case I suggest that you discuss your prognosis with your PM. Ask him whether he thinks that he can treat the headaches. A good doctor will admit when he is not the best person to help you.
If you decide to see a headache specialist and need help finding one be sure to let us know. Keep us posted and best of luck!