Hello and welcome to HealingWell. I think Shy has advised you well. You are at a point in your life where you can see that change is coming. Now days there is a lot of stress associated with being a senior, choosing what your going to do when you graduate, your friends will all be going in different directions but also you will be starting on a new adventure of your own.
Life never remains the same and no matter how much we would like it to things change. Change is scary. Change can be awesome too. So keep an open mind and don't expect the worse.
I agree tyou should see your Physician and start back on the Lexapro and go the distance in giving it a chance to work. 4-6 weeks is the normal time frame for most antidepressants to be at their full potential however some people may take 8 weeks...........everyone is different.
Do you have someone to talk to, your Mom or another person you trust. Coming here and talking is a good way to get out your feelings but let them out. Don't bottle thos feelings up and pretend like your OK when you feel sad inside. You recognize that something is not right and that is the first step to healing.
Again a warm welcome and keep posting.