In my opinion you are not able to clean them because there probaly has been calculus(tartar) formation on them.If you are into tobacco consumption of any form,that could worsen things too.
Next Steps
You must visit a dentist and get cleaning and polishing done.
Health Tips
If these yellow stains keep coming up,i would recommend you get scaling done every four months.Maintain them well and there would be less damage and hence no sensitivity.