While I do not practice law in your State, I can give you some general information that you will need to check with an experienced criminal defense lawyer admiited to practic law in VA.
Assuming that you are referring to a conviction in State Court, you will need to check the State Expungement Statute in VA to determine several things. First, does the exungement statute require any 'waiting' period before you can apply for an expungement. Some statutes, like those in NJ do require a waiting periood, which genrally runs from the date you completed the sentence imposed (not the day you were convicted).
Second, is the specific statute under which you were convicted listed as an offense for which there is no expungement. For example, in NJ, the Possession of Drugs can be expunged, after the completion of the waiting period. On the other hand, the Possession of Drugs with the Intent to Distribute is barred from ever being expunged by the NJ statute.
These and other related issues need to be discussed with a lawyer who is familiar with the VA law applicable to these types of petitions.
This answer does not, nor is it intended to, create an attorney-client relationship or constitute attorney advertising. Rather, it is offered solely for information purposes. Since the facts of each case are different, it is critical to consult with qualified counsel with whom information can be shared and assessed under an attorney-client privilege, so that competent advice can be obtained on which you can make informed decisions.
I wrote an AVVO guide on obtaining an expungement in Virginia that is avilable if you click on my profile. However, in Virginia, you cannot expunge a conviction. You should first make sure that your case actually resulted in a conviction. Many times drug cases are disposed off pursuant to Va. Code Section 18.2-251. If this was the case, the charge may have been dismissed at the close of the case. However, this also does not necessarily mean you can expunge the charge. There are a number of cases from the Virginia Supreme Court and Virginia Court of Appeals which say that if someone pleaded guilty, they cannot expunge the charge even if it was later dismissed. It is something that you should talk to a local attorney about..