I started lexapro 10mg yesterday, a friday. i am feeling way tired, unmotivated, lethargic. can i take half a tablet until monday when i can call my doctor? i am very lightweight when it comes to medications. i feel 10 is too much to start on?

There would be no harm, no withdrawal, in doing so. It is, however, a surprise that 10 mg. of Lexapro would have such an effect. It is not impossible, just very unlikely. The risk is that you are mistakenly delaying effective treatment -- but your doctor will be in a position to really say that you are having that side effect. In any case, There is nothing that is harmful in what you propose.