I am on a new med called lexapro, i am depressed and i am worried that this medicine wont help?

I am 17, i have been chronically depressed for a few years now. Doctors have had me on and off meds.. on different ones at the same time they have tried everything. I have been on Lexa-pro (Escitalopram) in the past but not by its self. i have done my research and i get out of it that it helps you think happy thoughts and when you are "able" to be taken off of it that you should be able to continue these "thoughts" or the get up and go attitude not moping around , depressed. I have also seen/ read a thing saying it causes damage, and doesn't use the serotonin in your system. causing it to fade or not be recycled. should i be concerned? Also another thing, be cause this does what it does how it does it (cant explain it) am i going to need a higher and higher dosage to keep me "high" or not depressed? If anyone is on this med for depression or anxiety please help me.