Fine thin hair loses volume after a few hours — what am I doing wrong?

Hi.

I have fine, light-colored and not very thick hair. The problem is that after a few hours my hair looks really bad and flat, and I can’t understand why.

My routine:

• I wash my hair with Burt’s Bees baby shampoo
• I don’t use conditioner
• I apply a sea salt spray (Davines)

Right after washing and blow drying, my hair looks good and has volume for the first 1–2 hours. But after a few hours, the volume completely disappears. My hair doesn’t look greasy, just flat and lifeless.

What could be the problem?

Is it over-dried? Or too soft? Or something else?

Has anyone had a similar issue?