My doc prescribed zovirax cream for genital herpes....but I read that it should not be used for that

I don't think a topical application of Zovirax will help much for Genital Herpes, you need something systemic. (It may help to some degree but I don't think it'll give full suppression).

I'm sorry I don't know why your doctor gave this to you. May be they have used it for some other patient and it helped? If your symptoms persist go back to the doctor and ask them to give you the medicine to be taken orally.

The link below has names of medicines which may be used for Genital Herpes.

http://www.drugs.com/condition/herpes-simplex-suppression.html