I believe you are asking whether you can reopen your conviction after you have already been sentenced pursuant to a plea agreement. If so, unfortunately, I don't have very good news for you.
It is very difficult, almost impossible, to get a plea back after the sentencing, because at the time of any plea, the judge does his best to make an in-court record to make the plea airtight in order to avoid just this situation.
Your own plea allocution would be used against you to show that you made a knowing and voluntary waiver of your rights in order to accept the deal you accepted.
So you need a strong legal basis to succeed at a post conviction remedy. "Buyer's regret" is not a legal basis to take a plea back. Nor would you ever want to say that you took a plea only to avoid going back into jail because a drug test would have revealed you were still using. These are not reasons enough to reopen your case.
You'd need to have a Constitutional argument or an argument that you were denied due process of law. I don't see that in your fact pattern.
Also, there's also one more thing you'd have to consider. Let's assume for the moment, just for the sake of argument, that you can get your plea back. The case goes back to what it was before. You will have to go to trial because in my experience, the state won't offer you another deal. And the judge cannot reduce the charges. So, if your case was reduced for purposes of a disposition, getting the plea back would reopen it to what it was before. And a trial for that was exactly what you most wanted to avoid.
However, if you're able to afford a post conviction lawyer, you can talk to him at length about your case and see if he can find a good basis to try to reopen your matter, such as the ineffective assistance of your original lawyer. Just keep in mind that your prospects for success are low and that you may end up not improving your situation but making it worse.
If you don't know where to find a Nevada post conviction lawyer, you can try the Nevada Bar Association's Lawyer Referral Service.