Nausea is a common side effect of Lexapro and many other antidepressants. If you can tolerate it, stick with the medication and hopefully the nausea will go away in the coming weeks. If it gets too bad to tolerate, which happens sometimes, you can always stop the Lexapro and try another medication.
Figuring out a good antidepressant for an individual is guesswork, because everybody responds differently to them. I've tried three over the years. One gave me some nausea at first, but it went away after 3-4 weeks. Another made me sick as a dog, just miserable, and I stopped it after one week. A third one gave me practically no side effects at all.
The key is to be patient in finding one that works best for you.