@Usha,
Here are few general gems which are found to be effective for Acne problem (in general terms without going much deeper into astrological details).
1. Rhodochrosite: You can carry rhodochrosite as a touchstone.
2. Aventurine: Wash your face with aventurine water every night. You can make “aventurine water” by placing aventurine either in rain or well water for a day. Women should wear jewelry made from aventurine.
3. Amethyst: It has also been used for acne related problems. You can either drink or wash your face with water which is “charged” with amethyst.
Although, your problem cannot be solved by a gem stone alone as your body has a blood cleansing need, constipation and acidity.
I recommend you to meet an ayurveda specialist or a naturopathy practitioner and get your digestive system cleaned up.
Avoid eating fried foods (spicy foods) and dairy products such as milk, curd, cheese, butter, paneer, ghee etc. for a month. Detox your body by consuming juicy fruits and vegetable juices of the season. Stop eating breads and wheat related products for a month. Take a diet of long grain white rice, daal and other grains ( but don’t eat wheat and white flour).
Maintain a strict diet on the above lines for a month and see the difference. You will surely look charming, beautiful and radiant.
Wishing you good luck, May God bless you and above all?
CHEERS