Man I'm glad I read this post. I might be able to help out. I use to do car sales, and say what you want about sales man but it's hard to get up in the morning be positive before 8am and talk to perfect strangers then sell them a $40,000 or $80,000 vehicle. So I know where you are coming from. I'll warn you this post could be long but worth it.
Okay so here's the thing. It's all about your Positive Mental Attitude (PMA). Here's an example of what not to do; "If you get up out of bed, and stump your toe, you think to yourself it's going to be one of those days. Then you go to the bathroom and cut yourself shaving, man it's going to be one of those days. Then you head outside and it's cold, man it's going to be one of those days. I've been there, hell we all have, but what seperates us from successful people is a positive attitude. It's something learned as a habit for the most part.
Here is what to do. You wake up, first thing after hitting the alarm clock, jump out of bed and smile.

It's contagious habit to get in smiling. Then you get out of bed and stump your toe. It doesn't matter I'm going to have a great day...You cut yourself shaving, ha ha little devil razor, you can bring me down. You look at yourself in the morning in the mirror, and say, "Damn you're one good looking SOB you know that!" Yes, I do this! LOL. Anyways, you need the positive attitude and you have to work at it, that its going to be a great day, good things are going to happen, and you're going to make them happen. It's tough but its the mindset that differs us and successful people.
*Try to eat a good breakfast, not just a poptart, and do a light workout in the morning or stretch. When you eat good and do something physical like that your body gets more endorphins.

May even have to getup a little earlier to fit all this in. Make sure to get atleast 8 hrs of sleep. Again, this takes work.
Regardless of what happens keep smiling. It's hard to feel bad when you are smiling all the time. You'll notice others around you will be smiling more also. It's a great disease called happiness!
Talk to your friends at the bus stop about whatever you want to, you're the fun positive guy. Talk about sports, weather, celebrities on the fritz, computers, Internet, School Rumors, how the bus driver smells, whatever, just get use to talking.
Believe me when you are happy you want to talk to people and share the feeling. And also believe me when I tell your grumpy people hate this about us! You can do this, I know you can. I did it, and I'm the laziest person I know, I had an excuse for everything, but not giving myself the happy life I deserved!
GOOD LUCK, and let me know how you're doing!