By all means don't improvise! What about your previous doc, was he a psychiatrist? Definitely you should keep in contact with him to decide development of the treatment.
And the new doc? Not prescribing a medication because it is expensive sounds very unprofessional. Not giving instructions about what to do with Lexapro (probably it should be stopped gradually, if stopped) sounds even worse. You need a serious doctor and has to be a psychiatrist. And the treatment must be planned.
My advice in these situations is: find a pdoc you trust and follow up with him.