Depression Forum - School... Feeling Loss of Intelligence/confidence

Well, this is basically my story regarding school.

Grades 9 and 10 I was a bright kid, very smart and always confident in class, I knew I could easily do well in anything as long as I put in effort, and I did.

Grade 11 I began to slack off a bit, started drinking here and there and just began smoking pot. I didn't try very hard at all.

Grade 12 was the worst... This was supposed to be my last year of high school. However, I was so changed by this time. I started smoking a lot more weed, every lunch I would meet up with friends to smoke. I even had a part time job which I knew got in the way of school but I was making money to support my fun like drinking and smoking so I didn't bother quitting. I also used to skip class very often. I did not apply to college because I didn't want to go. I did not apply to university because I did not have the marks for it.

Okay so... I decided hey, i'll stay back another year in high school and just upgrade my marks for university. Nothing wrong with that, so many people do that and not everyone goes to university right away. So I started school again, basically my fifth year of high school.

But a week before school had started, I witnessed the most tragic experience of my life. I had saw my own uncle, whom I loved and lived with for a long time dead in my house because of drug abuse, the most shocking experience ever of my life. This experienced ruined me...

When I actually started going to school, I was too depressed to focus. I'd always skip just to get high and forget about my problems. This only made the issue worse... I went from smoking pot, to popping pills, snorting cocaine, trying a variety of drugs all year because I just got so deep into the whole drug thing. I wasted a year of my life on drugs, depression, anxiety, just horrible things. Because of this, I had a lot of anxiety and panic attacks.

Last year was my biggest low of my life ever. I didn't smile much, I was never genuinely happy, and I was ruined by drugs.

Okay so now... SIXTH year of high school and i'm 19 years old now. Today was the first day. I no longer do any drugs like before, except drink occasionally. I finally feel like I have a clear head now.

To me this is like a second chance, or my last chance. Theres so much pressure on me right now. I feel like I can't make any mistakes at all throughout the year and I have some hard courses. I only went today for the first day and I ALREADY lack confidence. I feel like I won't make it, its just making me so depressed. I don't know what to do. I don't feel like the smart kid I used to be and it makes me sad. I haven't been in school for so long that it feels so weird and different now. I was so nervous that I came home and my stomach was aching, I felt like I needed to throw up, it was that bad. I feel like such a loser sometimes...

Any advice?