Which teeth whitening product should I use?!

My dentist gave me one where it is a tray and you put the goo in it and where it on your teeth as long as you can, but the goo never stays in the tray and burns my gums so I can never keep it in very long. It whitens my teeth, not a lot though, and it doesn't last very long. I'd like something quick, that works, with no goo.