What causes it? How do I get rid of it?

I've never had dandruff before and I'm so confused.

I noticed my boyfriend definitely had it, but now I have it too! I know it's not contagious... But we use different shampoo.

I wash my hair twice a week with coconut and vitamin E shampoo and conditioner. I recently started using leave in conditioner on my ends.

Is it the water? Shampoo? Frequency of washes? The weather? Pillow cases? Whaaaaat????

Its gross 😭