The technical, hence expensive, book on the subject is Travell and Simons's Myofascial Pain and Dysfunction: The Trigger Point Manual. FWIW, Janet Travell was John F. Kennedy's doctor.
The practical manual (under $14 at Amazon) is Claire Davies's The Trigger Point Therapy Workbook: Your Self-Treatment Guide for Pain Relief.
You can do more good with this book and a firm tennis ball than a physician, a surgeon, and a chiropractor could do with your whole bank account. And you'll avoid the potentially fatal side-effects of pain-killing drugs.
These drugs are not for muscle pain. They are for chronic joint pain as well as the associated problems with other collagen diseases.
Except the trigger points are really called enthesiopathies. T & S's maps are 25 years out of date.