If I am currently on a pre-trial diversion for possession of a controlled substance, am I able to get my background expunged sooner than 5 years?

Usually the whole point of a pre trial diversion program is to avoid having a criminal conviction entered upon a successful completion of the program. If you failed to complete pre trail diversion then a conviction can enter on your record. Check to see if this conviction is actually appearing on your criminal record. If it is, then most states will not allow the conviction to be expunged until five years from the date of sentence.