the tonsils may have little holes or crypts in them that can trap food and other debris. sometimes this debris can calcify and create a little stone-like mass called a tonsilliths (tonsil stone). since i have no way of seeing your little white spot first-hand it would not be possible for me or any medical provider to be able to give you an exact answer based solely on your brief description. it is possible to have localized infections so since you are concerned it would be in your best interest to have your tonsils examined by a health care professional.
i have a white spot about the size of a large grain of rice in the back of my throat on my tonsil of the left side. its a small white spot but it is very easy to see upon emamination. i have just gotten over a cold that did start with a very sore throat but that was about a a week ago now. there is only a spot on one side of my throat. i'm worried its some kind of infection. i can touch the area with my tonge and it is much warmer on that side of my throat than the other side. it is mildly irrated.