A CA DA has one year to file misdemeanor charges against you. It is odd that none have been filed yet because duis are usually vigorously prosecuted. Do NOT call the DA and ask the status. If he intends to prosecute you'll eventually get a letter in the mail. In the meantime hold your breath.
The DA has one year to file on a misdemeanor. We are seeing more and more counties take longer periods of time in filing charges on DUI cases, so this is probably nothing out of the ordinary. You should contact a DUI lawyer who regularly practices in the county you were arrested in. This attorney will be able to best advise on what is going on with the DA's office, and will in most cases give you a free consultation on fighting your case.