I think I'd be a little suspect of my doctor (or ANY, for that matter) who more or less blew off the MAIN reason I'd come to see them in the first place. For him to have "hastily" prescribed Lexapro, I'm guessing that much of your conversation centered around depression and anxiety. If that WAS the case, I'll give him the benefit of the doubt, and go with the assumption that he saw your headaches as a simple adjunct to the depression/anxiety. If you feel that you have been wrongly diagnosed, then waste no time getting back with him to discuss this in greater detail, making sure he takes your headaches into greater consideration. Perhaps a visit to a neurologist would not be out of the question..........you could certainly broach the idea to your doc and remember, it is your right to request a referral to a specialist. I think you first need to rule out any underlying cause for these headaches, then tackle the depression/anxiety issue.
Keep up posted, OK?
Peace
Greenlydia