Why is my hair falling out?

My hair is thick and quite wavy, it's at mid-back length. Since may, my hair is falling out and when I brush it, it's worse.
We always have hair falling, I know but now it's really a lot. My mother and my sister also have the same problem since may. We don't know why, there wasn't any stressful event, no change in our way of life. My hair is still really thick though.

Why do you think that my hair is falling out?
Why is my hair falling out?
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