Head Trauma as a kid, or just my anxiety?

Hey, my name's Jake and I'm 16 years old. I've always head extreme anxiety, in elementary school I'd always have bad temper and yell at the whole class. Now at 16, I still don't feel right and it's too the point to where I am going crazy. Everyday I'm on a long search on the internet to find what's going on in my head and what can help. When I think back to when I was very little, around 5 or 6, I always remember the time that a very large rock was dropped on my head. I didn't get knocked out but it was very serious and had stitches and stayed in the hospital for a while. And now I think that is the reason. Here is what is going on in my head... I think too much of what other people think of me. Or just think to hard in general. I always feel like things are awkward, when they're not. Example: riding around in my friends car, I role my window down, I think he thinks I'm weird for having my window down, or he doesn't want it down. Even though he probably doesn't even notice my window is down or even cares. My thoughts often feel "cloudy" and I get off track easily. I feel like this issue is holding me back from doing some fun things and having a great life. I used to be a real good student, but now my grades are dropping extremely. I often find myself looking in the mirror, it's like I have to. I don't know why, but I think it's me trying to find who I am. It's like I have no personality. When I see people, on the street, in school, I try to see my self as that person, I do this as a way to really see how un normal I am. I also always think myself as another person, and if I saw myself so I get a point of view of what I look like and act. I am way overly conscious of my looks. When ever I learn about a new disease, or disorder, I focus all my energy on that and I think I have it. I once convinced myself I was mentally retarded. I just wish I could be somewhat normal in the inside as everyone else. I know you're suppose to accept who you are, but I think this is something that needs to be dealt with. I have made some very good healthy choices by trying to eat right, working out, and even joined my school's football team in hope that I can be mentally healthy. It's helped a little, but this is driving me crazy and can't see myself living like this for more than another year. I have an appointment in about a month with the therapist. I was just wondering if anyone could give me a head start on all this. I tried to explain it as well as I could and any advise or information would be appreciated.