Lakenheath station only has a limited weekend service, nothing at all during the week.
Brandon has a proper service and is about the same distance from RAF Lakenheath as Lakenheath station, there may even be buses from Brandon to the base.
I assume you do have some sort of idea if anything is flying from Lakenheath or Mildenhall, it would suck to make the journey and find the USAF were having a quiet day.