My doc says i have horners syndrome is it commonly benign commonly? one pupil doesn't constrict as much as the other

Yes, benign: Horner's syndrome is usually benign, and may resolve on it's own after a few weeks or a few months. It can be troublesome for many patients when eating, or during social encounters. Very rarely, a cancer may be responsible, but for a young lady it your age group this is extremely unlikely. Keep following with your doctor, but in the meantime focus on your health and the things you can control.

Is it ONLY the pupil: In order to diagnose Horner"s you must have the other symptoms. If it is only the pupil, we look for entirely different things. WHAT DID THE DR TELL YOU???? There are a variety of different things to consider if you have only pupil change, and an entirely different list of considerations if it is Horner's. Some of them are important and serious.