When does Lexapro work???

Hi ladies. I've been on Lexapro for generalized anxiety disorder for almost 3 weeks. I am only on 5mg and take it every night before bed.
I haven't really felt a lot of side effects just a bit of nausea and tiredness. 
I'm in a 14 month program for medical assisting and I end this September of 2016. My anxiety prevents me from doing so much like going to school, going out to dinner, going to events, and basically anything that involves leaving my house!!
I'm just wondering how long this medication takes to kick in? 
I'm missing a lot of school I'm scared I might not pass but I physically don't think I could sit in class from 5pm-10pm with how I feel. I honestly feel like im dying 😑