Congratulations on your recent breast augmentation! Itching is a common symptom after a breast augmentation due to the stretching of the tissues and the normal healing process as long as there is no accompanying rash. I usually tell my patients to take Benadryl for relief. I recommend you call your surgeon's office to see what your doctor recommends. Best of luck with the rest of your recovery!
During the healing process after your surgery there are some phases that your tissues go through, the first one is inflammation which consist in the liberation of certain molecules that may result in your described symptom, I recommend taking anti-allergy medications to ease your itch. This group of medications includes over-the-counter drugs that don't make you sleepy, such as cetirizine (Zyrtec) and loratadine (Claritin), or those that make you sleepy, such as diphenhydramine (Benadryl). The ones that make you sleepy can be particularly helpful at night if your itchy skin keeps you awake.