Flax seed is only valuable for its omega-3 content, but that omega-3 is the ALA form, which is less usable than the DHA form. DHA can be found in large amounts in fish and other seafood.
My father and I had migraines before going paleo. Doing an ultra-low carb ketogenic diet for awhile seems to be the best method to kick them. Adding in some fish can't hurt either.
As a migraine sufferer, I can sympathize with your need for a remedy. I have tried nearly every preventive and incidental herb/drug on the market. I have been gluten free for a year and a half, but still occasionally have migraines. I eat mostly paleo (always gluten free), try to get plenty of sleep and keep stress to a minimum. MSG is a huge trigger for me (migraine in <30 min), so I have to be really conscious about eating out.
In addition to lifestyle changes, I have also added a few supplements to my regimen. NOW Foods makes a combination formula of Butterbur with Feverfew. 2-3 of these per day have decreased the frequency and severity of my migraines. You might also try increasing your magnesium intake. I supplement with magnesium orotate. I have not been able to tell any difference from eating flax seeds or taking fish oil.
I have also learned that frequently people suffering from migraines also have some adrenal and kidney weakness. My Chinese herbalist recommended Yanvive (Jin Kui Shen Qi Pian) about 6 months ago. By taking this twice per day, I have reduced the frequency of my migraines and improved my energy levels. I ran out a couple months back and missed it for a couple weeks. The migraines returned and I felt exhausted, so I know that it makes a difference for me. Needless to say, I ordered more and make sure I don't run out anymore.
I (accidentally) kicked my migraines by eliminating wheat from my diet. Whether this is because of phytic acid or gluten (I suspect the latter) - I don't know.
But I do know that it works.
I would avoid flax seed if I were you given that it is a seed.