For more information on myofascial pain, especially related to migraine and chronic headache, see the following references.

Migraine Brains and Bodies: A Comprehensive Guide to Solving the Mystery of Your Migraines by C. M. Shifflett.
More pictures and more information (see Head and Neck Pain on the the neuromuscular issues that may lurk behind a diagnosis of migraine. This is not a book about bigger and better drugs. It is about finding and eliminating root causes. See excerpts here concerning:

• General contents. From the traumatic life-shattering head injuries of Henry VIII and Elvis to mysterious hypothyroid symptoms and safer sports.
• What posture has to do with it. At home and on the battlefield.
• Mapping your pain. Where does it start? Where does it go?

Conquering Concussion: Healing TBI Symptoms With Neurofeedback and Without Drugs by Mary Lee Esty and C. M. Shifflett.
The title says "concussion" but we think of this as "Migraine: Book 2." Migraine and chronic intractable headache is an extremely common result of head injury and concussion. Emphasis is on results, what actually happens in concussion, the myriad and often unrecognized symptoms that develop, and best of all, how to heal the symptoms and return to a functional life.

Myofascial Pain and Dysfunction: The Trigger Point Manual originally by Janet G. Travell, M. D. and David G. Simons.
Since the deaths of both original authors, it is now known as Travell & Simons' Myofascial Pain and Dysfunction, by Simons, Travell, and Lois Simons.
This two-volume work is considered to be the Bible of muscular pain. The physician or therapist who doesn't have a well-marked, dog-eared copy with lots of yellow stickies, paper clips, stars, arrows, underlinings and highlighting, probably doesn't know muscular pain. (Pharmaceutical brochures are no substitute and muscle relaxants do not relax trigger points.) These are medical textbooks and although the prose is densely medical, the summaries and pictures alone are worth the price of admission. Volume 1 addresses the upper body, and Volume 2 the lower body.

Fibromyalgia and Chronic Myofascial Pain by Devin Starlanyl, M. D.
Physicians have long dismissed fibromyalgia as a mere women's disease ("and these women are CRAZY!") That is starting to change, in part due to the development of far too many tests that reveal clear clinical abnormalities behind the pain, and in large part due to Starlanyl who is a doctor herself -- and suffered from severe fibromyalgia. Fibromyalgia is still commonly confused with myofascial pain syndromes. (Nearly every long-time beautician I have checked has upper back and neck pain with severe trigger points in her trapezius -- and a diagnosis of fibromyalgia). You can also suffer myofascial syndromes with the beginnings of fibro, or have fibro with myofascial syndromes and trigger points. To clarify the difference, Starlanyl's book includes the superb trigger point and pain referral diagrams from Myofascial Pain and Dysfunction: The Trigger Point Manual.

The Trigger Point Therapy Workbook by Clair Davies.
Davies was a piano tuner nearly incapacitated by shoulder pain. Ultimately, Travell & Simons' myofascial techniques were the only thing that helped and what ultimately resolved the problem.
(I was a pianist and field geologist nearly incapacitated by migraines -- in part, I suspect, due to neck trauma from the poorly fitting backpacks and equipment of 30 years ago, designed for Tall People only. Hot tip: NEVER wear a pack that forces your neck into a head-forward position!)

At any rate, Davies wrote the book I wish I had written back when I first studied myotherapy, hoping to relieve my pain, many years ago.
The material is solidly based on Travell & Simons, but emphasizes self-(rather than clinical) treatment techniques. If you lack medical background, use the Davies book with its clear non-technical English in conjunction with Travell & Simons for its terrific illustrations.