## Core Concept
The question revolves around a patient presenting with persistent symptoms of headache without any identifiable organic cause. This scenario points towards a **psychological or psychiatric condition** rather than a neurological or medical one. The key concept here is to differentiate between physical symptoms that have a medical explanation and those that may be manifestations of psychiatric disorders.

## Why the Correct Answer is Right
The correct answer, **D. Somatic Symptom Disorder**, is appropriate because the patient presents with a persistent headache, insists there is something wrong with her head, and has had multiple consultations and investigations without finding any medical cause. Somatic Symptom Disorder is characterized by one or more chronic physical symptoms (e.g., pain, fatigue) that are distressing and result in significant disruption of daily life. The symptoms may or may not be associated with another medical condition, but the patient's thoughts, feelings, and behaviors related to the symptoms are excessive and not in proportion to the severity of the medical condition.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but typically, other psychiatric conditions could be considered in the differential diagnosis, such as anxiety disorders or depression, which might present with physical symptoms. However, the specific presentation here aligns more closely with Somatic Symptom Disorder.
- **Option B:** Similarly, this option is not provided, but conditions like Factitious Disorder (where a person fabricates symptoms) or Malingering (where a person intentionally produces false or grossly exaggerated physical or psychological symptoms) could be considered. However, the description does not strongly support these diagnoses.
- **Option C:** Again, without the specific option provided, it's hard to directly refute it, but generally, conditions like Hypochondriasis (now referred to as Illness Anxiety Disorder) could be considered. While this patient is concerned about her health, the presentation seems to fit better with Somatic Symptom Disorder due to the focus on the symptom itself rather than fear of having a specific disease.

## Clinical Pearl / High-Yield Fact
A key point to remember is that patients with **Somatic Symptom Disorder** often have a high level of healthcare utilization, as seen in this case with "several consultations" and multiple investigations. The challenge for clinicians is to balance providing reassurance and managing symptoms while avoiding unnecessary tests and treatments.

## Correct Answer: D. Somatic Symptom Disorder.