Teeth whitening

I also want to get teeth whitening because my teeth are yellow, and I'm a bit cautious about smiling with my mouth open. I'm worried someone might see. I'm also concerned that it might look bad externally. So I tried whitening toothpaste, but I didn't see much effect. The pictures say that after a few days of use, teeth become whiter, but I wonder why that doesn't happen to me. I'm also worried about my yellow teeth, so I want to try teeth whitening, but I'm curious about the cost and how long it lasts.