@Usha kulkarni,
Regarding your Acne problem (in terms of astrology); it usally signifies that your blood significator planet has been associated with a malefic planet. And the planets which usually give out these issues are Mars and Saturn.
To come up with any conclusion, it would be really good if you could share your birth details like date, time and place of birth here (with us) and we will certainly help you in figuring out the astrological aspect of this problem and also suggest a cure to your problem.
Apart from that; Yes, gems have been used as medicine since the ancient times. But for it to be truly effective, you will require purest gemstones available. Also, many modern day medicines include gems as thier ingredients.
Hope to see you back with your birth details
GOD BLESS!!!
Srinivasa Temkar