Jalapeno, typically it takes four to six weeks for an SSRI to start calming you. Sometimes, it can be less. You can expect to be a bit jittery when you first start taking an SSRI. Usually, your doctor will prescribe an anxiolytic, like klonopin or xanax to calm you down during that introduction time.
5 mgs. of Lexapro is a very minimal amount, so you should have very little side effects from that dosage.
Wishing you peace and calm as you ecover,