Tooth discoloration

My teeth have become discolored.

I'm not sure if it's because of coffee, candies, or something else, but showing my teeth and smiling feels uncomfortable.

I get a scaling once a year, but should I also do teeth whitening?

Are there any products that whiten teeth? Has anyone tried them? I'm curious if they are effective, and if I get whitening treatment at the dentist, how many sessions would I need to see results? Also, I'm wondering about the price range.