I'm not going to have good news for you.
It's nearly impossible for someone to take his plea back, if he's already been sentenced and done his time for the crime. This is because judges do what they can at the time of the plea to make sure that the plea is airtight. They generally ask a handful of questions one of which is, "Are you pleading guilty because you actually are guilty?" Judges won't sign off on the plea unless they have been told by the defendant that the defendant is actually guilty of the charges,
While all of this is going on, there is a court reporter who is taking down the judge's questions and your answers. Those answers will get used against you to show that you were indeed guilty as charged, and will be used to deny your motion to overturn your conviction.
You also had a window of opportunity to file an appeal back three years ago, if you felt your lawyer didn't advise you properly. But notice would have had to be filed within 30 days of your sentencing. It is now too late to challenge your conviction on the grounds of ineffective assistance of counsel.
Illinois will not expunge or seal your conviction. The only two remaining ways to clear your name would be longshots.
The first would be to apply to the governor of your state for a pardon. A pardon would not erase your record, but the conviction would show as having been pardoned. That would be official proof that the state's highest official believes you've turned your life around. I am attaching the pardon information and instructions here.
The other option would be to hire a lawyer and see if he could get the case dismissed in the interest of justice.
A judge has the power to dismiss a conviction under principles of equity even when the law does specifically provide for that. A judge will use this power very sparingly and generally only to prevent an injustice. You would need to talk to a local criminal trial lawyer to see whether this is a viable possibility for you. The two of you would have to come up with some compelling reason that the court should ignore the statute under which you were convicted.
The DA would weigh in on this, and they would be very likely to object to the petition. If there was a complainant, he or she would be contacted and could oppose this as well. So this is not something you should try to do without a lawyer.
At this point, however, these are the only options you have left.