A betting man would say you need to find a new career. Hell, I say you need to find a new career. However, I guess there's still a chance that this is all overblown and you're actually not the pervert the law thinks your are. I mean, hey, you weren't convicted.
You have two big problems.
1) Schools find out. There is not a single medical school in the country that would accept you if they knew this. This is a HUGE deal, despite being an "expunged" or "dismissed" misdemeanor. You have a better chance of getting in with multiple drug convinctions than a sexual crime. It totally undermines the public's trust in doctors. Schools will almost certainly find out - Most schools use CertiPhi, a service that's extremely comprehensive.
Don't bother with a lawyer. This actually isn't really a legal issue. Plus, ten lawyers will tell you ten different things about this subject. What you need to do is run an FBI background check on yourself. This costs money and is time consuming, but you must do it. If anything comes up, you're done.
2) Licensing. This will be extremely State-dependent, so TALK TO THE STATE MEDICAL BOARDS.
Neither of these are steps you can skip.
Now if you'll excuse me I need to wash my hands.