Flaxseed questions

I've had chonric constipation all my life. Nothing has ever really helped. I know it depends on the individual, but in general does flaxseed usually help with people who have chronic constipation? What forms work best? Is there any other natural things I can take to help the flaxseed work better?
Also, where can I buy safely buy it online? I've seen several independent sites and I am afraid to buy something I'm going to put in my body from somewhere I don't know.
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