Stress is one of the most common triggers of migraines -- that's why massage is one of the recommended therapies because of the stress relieving factor. When the body is under stress, it reacts with a "fight or flight response" which releases chemicals in the brain that can provoke migraines. Migraines can last up to three days (ouch).
Interesting fact: More than 45 million Americans seek medical attention for severe or chronic headaches.
I guess this doesn't include the number of people who NEVER seek medical help for them, so there's probably way more people. If you have not seen a doctor about your persistent headaches, you should. They will do a physical evaluation and have you describe your headache history. You want to give as much detail as possible. Don't worry if you haven't figured out all the triggers.
When you are experiencing a headache specific nerves of the blood vessels and head muscles are triggered and they send pain signals to the brain. Migraine headaches are related to pain in the mid-brain area where blood vessels are constricted and dilated along with other hormones that cause painful pulsations. They are often accompanied by nausea, vomiting, and sensitivity to light or noise. Migraines, because of their debilitation, are now considered to be a neurological disease with a hereditary link.
Interesting fact: There is a family history of migraines in about 90 percent of migraine sufferers. So if your parents don't suffer from migraines, ask them if their parents did because there is a good chance that one of them did.
References: https://migraineresearchfoundation.org/about-migraine/migraine-facts/; https://www.ihateheadaches.org/headache-statistics.html