I went through this. When I left for college I was completely unprepared to live on my own; eventually I got depression and ended up crashing pretty hard. I got kicked out of school because I was in a mental ward and the school determined I was "a danger to self or others" and used that as an excuse. I'd been failing before that.

So... fast-forward a couple of years; I've been trying to get jobs and getting fired because I can't do the job. Finally I managed to get back to school thanks to the vocational rehab people determining that the only thing I'm good at IS school, so it's my only chance at getting a job. (They did neuropsychological testing.)

Been back at school since September. Passing my classes.

What I found out:

1. Asking for help is good. Try the disability service office; you can often get in for emotional problems if you haven't got a learning disability. They can often give you things like tutors, note-takers, or organization lessons. They will not give you anything that gives you an advantage over other students. If you can't get in there, most schools have tutoring services, or upperclassmen willing to tutor for the price of a few dollars an hour or even for free as part of a campus organization mentoring or "help room" proram. Heck, you can probably bribe some of them with your mom's home-cooked dinners.

2. Telling yourself you're stupid or lazy is not a solution, so it's counterproductive. (I have not yet completely managed to stop it... but I try.)

3. Keep your class load at an absolute minimum. Plenty of people take an extra year or two in college, and no employer will look down on you for taking longer to learn things thoroughly. If you start getting A's left and right, you'll know you can increase the load a bit. Not too much--just by one class.

4. If you find yourself calling yourself stupid or lazy, stop it, step back and think, "Exactly what is the obstacle preventing me from getting this studying done?" Identify the problem, describe it, and you can often start looking for a solution much more easily.

5. Do you have any really big weaknesses? For example--do you have trouble reading? Concentrating? Doing math? Memorizing? Take those into account when you study. For example, I have a lot of trouble memorizing information that doesn't easily connect to other information; so I deliberately learn everything in a way that lets me connect it. Plan strategies to get around them instead of just telling yourself you're stupid.

6. Keep your overall stress level down. It's murder on your grades.

7. Learn to break big tasks down into smaller, not-so-overwhelming chunks.

8. Don't be afraid to drop obligations. School is your number-one priority, so you can say "no" without people getting upset about it, generally, if you say "I'm having trouble in school and I need to concentrate on studying."

9. Coffee helps many people concentrate. Try it--but not too much in the evening, if you can help it, because sleep is when you process and store the day's new information, and you definitely need sleep too.

It's summer now; have you considered getting a summer job and squirreling the money away so that you will be able to rent a place if your mom does kick you out? Safety nets are important.