Hi. The cause for pimples/red marks on one side of the face is usually something that rubs/touches one cheek skin more than the other cheek. Examples for that are sleeping on the right side (right cheek is rubbed on your pillowcase), leaning on your hand touching the right cheek or over using your smartphone. These things can be corrected. Washing your pillowcases more frequently, sleeping on your back, not touching your face at all and lastly using your speakers or earphones.