I'm sorry to hear your story, mine is quite the opposite:
Within two days after leaving the hospital (7 days after my surgery) I was already able to take Maximum Strength Tylenol and feel pretty decent (though not 100%). 3 years later I am in great shape, and in many ways I feel like the experience was very improving, mentally and spiritually. However, I have had a harder time dealing with seizures and the medications I've had to take because of them. But it's not all bad, I'm convinced that one of my anti-seizure meds (dilantin) gives me great orgasms all the time...so you have to take the good with the bad, y'know?

best,
Otterbop

Usually, "pain in the brain" after surgery is associated with either the loss of cerebrospinal fluid, or with the mucsular connections that had to be cut through in order to access the site of the leision that nessecitated surgery. What you are describing is more likely to be migraine, which is a condition that can occur after any brain surgery. If that is the case, then narcotic medications could explain the protracted syndrome.

The initial surgery disrupted the dura mater, which, as you said, is in fact innervated for pain. This disruption caused a migraine syndrome that was likely short-term. However, the use of narcotic medication caused what are known as "rebound migraines" wherein when the narcotic wore off, the migraine returned with even more intensity then was experienced before. This sets up a cycle of worsening migraines that can be difficult to escape from.

Eventually, the pain receptors become hyper-sensitive setting up a chronic pain syndrome. The lessening of the symptoms that you are describing can be atributed to the return of the the dura to its original condition, which can take extended ammount of time. A pain clinic can help with the remainder of the symptoms and the de-sensitization of the dura to a normal state.