I dont claim to have any answers, but will give some advice.
Find whats missing and pursue it at all costs.
I am 29 yrs old and I've known what I was missing since I was your age.
Unfortunately, I pursued things like girls, good times, and drugs because they provided the more immediate fix.
I wanted and still want life, culture, beautiful achitecture...things that do not exist in midwestern united states. I am miserable here, but cannot leave due to the poor choices I made from the ages of 19-21.
My advice is to stay off presciption ad's and take some time to really, really think about what it is you want.
What are you going to college for? Is it what you want?
A major life change may help your depression and smoking.
If I could be 19 again, I would like to travel the world...I hope its not too late for me.