You bitting on your cheek and you don't figure it out in that time .

You may simply have bitten or burned your cheek. It also could be a canker sore developing. If it is not gone in 2 weeks then see your dentist.

Diet can also be a factor, and a diet that contains too much sugar, meat, and dairy can affect the skin (I found dairy to be a huge factor in keeping my cheeks clear). Finally, hormonal changes, medications, stress, and anxiety can also contribute to cheek spots, and these can cause blemishes in other areas too.