You may want to give yourself a break. I sense a high drive and ambition in you - and of course, that's not a bad thing - however you may be beating yourself up if you don't have perfect performance. Geez, can't a working mother who makes the primary income, as well as raise two young children, shuffle patients, fill out insurance forms, focus on what's best for the patient, make sure the kids go to bed on time, whose worked hard in school to get a good education, be allowed to not be so hard on herself?
You'll need to give the Lexapro a few more weeks before you really notice a difference. As a general rule, antidepressants for anxiety disorders may take up to 12 weeks to take into effect. The medication will do one primary thing, it will help you manage your anxiety levels, and as a person working in the medical field, there's nothing wrong for a sick patient to ask for help. The aim of the patient is to get better, not beat themselves up for getting sick.
Of course, in dealing with anxiety, the type of thoughts we think, in addition to how our brain responds to our thoughts, is just as important to consider. Since you're getting help with a cognitive behavior therapist, you'll benefit from someone, who can train you to think differently about your situation.
All perception - including your perception of your current job and how it makes you feel stressed - is based on how you direct your thinking on how you think and feel about the situation. One of the tenants of cognitive behavior therapy is to shift your focus, and writing exercises are part of that shift.
You may want to write out lists of what is working in your life right now. For example, if you spent twenty writing a list of what you do have -- a supportive husband, a nice building to work in, two kids who look up to you, a stamp of approval that you work and raise kids -- you can shift your focus on what is working, instead of what is not working in your life.
There are other cognitive behavior exercises I could recommend, but the Book of Positive Aspects (BOPA) can be a valuable tool, in conjunction with the medication, since it forces you to redirect your thinking, without necessarily having the situation change immediately.
In other words, you don't have to feel confident, until you leave your job. You just have to direct your focus, and still feel good, while you are at your current job, now.