I'm glad that you're giving meds a chance….
I'm sorry that you didn't have a positive experience with your prescriber, but I agree with Littlepaw that the fact that he was willing to admit that he didn't know the answer to your question is actually a good sign.
Please give the lexapro and the prescriber time to work for you. The dosage of the lexapro will need to be adjusted, or a different med may end up being a better fit for you in the end. And you may find that your relationship with your provider gets more difficult over time. If that's the case, you can get a new one… you're not married to him.
Good luck Sam, and keep us posted