The human body is made asymmetrically and all skin diseases affect once side worse than the left and very rarely only one side. Nothing to worry about. This is well recognized. The itch and swelling however are something different. It suggest and allergy to something you are applying (? maybe to teat the acne itself). Can you think of anything you do prior to the itch appearing?
I would suggest using Isotretinoin gel once daily along with your treatments as that would definitely help clear up the acne. You need a prescription for that though.