Hii... If You have a yellow layer on the tooth , That means the deposition of tartar on your tooth surface.. Black spot can cause food lodgement & pain in that tooth...That is why you are chewing from just one side & the other side of the jaw which is painful is not being used, that is why there is tartar deposition happened...

It requires clinical examination , please visit dentist for the same . Thanks!

Yellow layer on tooth may be due to plaque deposits on your teeth.get your teeth cleaned by a dentist. Black spot which pain while eating sweet or sour may be due to decayed tooth.get thorough clinical examination and xray of the tooth to fill/to do rct .

You need to get you tooth professionally cleaned and a radio graph to see the depth of the decay Its can be treated by fluoride application depending on radiograph.

From ur description it looks like u have deposits on ur teth surface and decay. U will need oral prophylaxis and x rays to evaluate the depth of that decay and treatment