Why does my straight hair always look horrible, no matter what I do?

I thought it might be wavy but it's not, it's straight.
Thick hair but very very thin strands. No matter the amount of brushing I do on daily basis it will take immediately and look very messy. It's natural, no coloring, treatments or heat. I used hair milk, oil, conditioners, none of them help. I'm so desperate my hair is ruining my otherwise fine appearance and my confidence.
Why does my straight hair always look horrible, no matter what I do?
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