Hi, Yellowish teeth can be either due to deposits ( usually tartar) or it may be internal ( like in case of Fluorosis ) . In some cases, the overlying layer of Enamel is worn off, so underlying layer of Dentin is visible, which is yellow. For the correct diagnosis, you need to visit Dentist and get it checked. If you can post some pic, then we can guide you further.

Solution to your problem is to visit a dentist & get a thorough check up  done. Yellowish  teeth can be corrected by cleaning & if need be followed by bleaching For Sensitivity the dentist will need to evaluate the teeth properly first before providing any solution.

Hi..you need to visit dentist. He might need scaling. Regards

Proper scaling and cleaning required mostly.  followed by bleaching and smile designing. Your photos would help me more.

1st is go for a scalling then go for vinear or composite

Please do visit a dentist to know the underlying cause.