If your teeth are hurting after using teeth whitening strips it's likely cause your teeth are more sensitive to peroxide that is used in the teeth whitening strips.
Normally for some people the teeth whitening strips should not hurt your teeth or cause any pain but it's not always a bad thing if your teeth do hurt for a bit after using teeth whitening strips to whiten your teeth.
After using teeth whitening strips you can brush your teeth using some Toothpaste for sensitive teeth to help remove the peroxide.
The peroxide is usually the cause of the pain when using teeth whitening strips.
You could also brush your teeth using some baking soda which also helps to get rid of the leftover peroxide on your teeth.
If your teeth are hurting after using the teeth whitening strips then you might want to try using some peroxide free teeth whitening strips next time.
Then your teeth should not hurt anymore.