How do I whiten my teeth?

Help me!! I want to whiten my teeth and I've tried whitening strips and they worked it's just it got to the point where they made my teeth super sensitive and my teeth would ALWAYS hurt. And here recently I've tried a whitener gel that goes in a mouth piece but that didn't seem to work to good, and I can not afford to get it done professionally. I don't see why these things I've tried arent working, my teeth are not stained. I don't drink, smoke, or anything. If you could help me out that'd be wonderful!!