I have white patches on both sides of my soft palate. they seemed to have turned yellowish today i quite smoking 2 months ago but noticed them before?

See your doctor: Leukoplakia, or white patches on the mouth or tongue, may occur because of cellular changes in the oral epithelium, or lining. At your age, i would not expect to see them, but if you were smoking for a long while, or unusually heavily, they may occur. They can be pre-cancerous and should be evaluated by your physician, who may refer you for further evaluation and treatment.

White patches: Any lesion in your mouth that lasts for more than two weeks mandates being seen by an oral surgeon for a proper diagnosis and treatment and\if necessary. Some lesions are easily diagnosed while others require a biopsy for confirmation. That is something that cannot be done over the internet. There are numerous possibilities, some benign and other not.