It's really hard to say because we're all different and respond to these meds differently. You could have nausea and a headache for a few days. That was my experience with Lexapro when I first started taking it.
How long before improvement?
Can you say when you started taking it and what dose?
It can take a few days to a few weeks for these meds to start working. I really wish I could give you a definite time. We really all are so different it's just really hard to say.