Your convictions cannot be expunged. They will also prevent you from becoming a lawyer. I am not sure about becoming a DEA agent but it doesn't seem iikely. You might wish to ask them directly.
First off congratulations on getting clean! That's great! I will let a more experienced attorney speak to the issue of expunging or sealing your record. Regarding becoming an attorney, ultimately, that decision will be made by the attorney registration commission of the state in which you want to practice. I don't think a felony conviction will necessarily foreclose that possibility. The most important thing is to be completely candid on both your law school and bar admission applications. The biggest sin in the eyes of the attorney registration commission will be dishonesty. Regardless of whether you are able to seal your convictions, your law school and bar admission board will most likely want to know about them. I would contact a professional liability attorney if you have any questions whatsoever about what should or should not disclose. Good luck!