How to look up a court record on myself. Criminal Records, Expungement

Hello. I would like to ask for some free advice. I am trying to look up a court record on myself from approximately 20 years ago. It is a petty theft/ shoplifting court record. I'm not sure if I was convicted of a first time offender infraction or a misdemeanor. All I remember is this lawyer talking to the judge and then I paid a $100 fine. It's all a blur to me now.....The two background checks I paid for on the internet did not come up with anything. I've worked several jobs since this stupid, horrible, embarrasing, idiotic infraction, but the offense has apparently not shown up on background checks. I'd like to find out exactly what my conviction was and when it happened exactly. When I went to the courthouse to look up the record, the clerks said they did not have any records on me. I gave them my social security number and birthdate and two forms of identification to assist them. Still nothing was on the computer. How do I look up this court record so that I may begin the process to have this record expunged or possibly sealed? I'd like to try to keep this matter private so it won't haunt me the rest of my life. I'm already a nervous wreck and I'm worried sick that this offense is going to pop up out of nowhere. In the meantime, I've been working nickel and dime jobs that don't require comprehensive background and credit checks. Thank you for any assistance you may be so kind to offer.