Hi, Katz, all of the above posters offered wise words worth considering seriously.
When I read about your situation, I really came up with a picture in my mind of a family -- all three of your individually and together -- stressed out to the max, with the extra added problem of everyone having big health issues that make life more difficult. You all obviously need some help to get through this stressful time. The question is, where do you start?
If your school has a counseling center, perhaps you could start there, asking if they have a staff counselor that could sit down and talk with you or if they could make a referral. If you're on disability, your health insurance probably pays for you to see a therapist. If you don't get a referral through school, you can probably get one by calling your primary doctor.
If you don't know what to say and can't get the whole thing out, try something simple like this:
"I'm having some adjustment and communication problems and would like a referral to a licensed psychotherapist or psychologist."
As Hvert suggested, you may also need some tutors or study groups to help you be more successful and feel less scared of making mistakes.
The thought that came into my head as I read about your situation is that you could really use the help of a psychotherapist who can teach you how to "fight fair" within the family dynamic. It sounds as if you and you dad have fallen into the trap of making low blows at each other, saying things that really hurt. It upsets you, gets you all ruffled up and afraid of making mistakes, and you know the arguments upset him for a long time, too.
Having a blowout with your parents every month or two is actually fairly common when people get to your age. I fought with my parents much more frequently when I first started college. We were at odds on many things and we got through it okay.
Your situation is complicated by the fact that you depend on your dad for care. He sounds very devoted to you and it sounds as if he's not dealing well with all the changes and stresses as you grow up and start college.
All these unpleasant words and stress have gotten in the way of your loving relationship. Underneath it all, it sounds as if the love is still there, as strong as ever.
If a therapist can help you learn to communicate better with your dad and to argue in a fairer and nicer way (yes, arguing can be nicer!) you may be able to convince him and/or your mom to participate in some family counseling sessions. It could help to smooth the waters, so that you, your dad and your mom all get along better and feel considerably less stress. A good counselor could help your dad understand that his angry words aren't helping the situation at all.
The place to start is with yourself. If you depend on your dad for transportation and have to explain to him why you're seeing a therapist, it's okay to tell him the truth -- you want to learn how you can communicate better because you want a better relationship with him and you want to do well in school.
That sort of thing can be hard to say because it can feel as if you're taking the blame for everything. But you're not. You're taking the responsibility for yourself, without getting his hackles up by criticizing him. In time, a good therapist can teach you how to approach your dad and ask him to join you in some counseling session.
I wish you the best of luck and hope you will come back and tell us how things are going. I'm sure other posters here at PscyhCentral have had these difficult relationships with parents they had to depend on for care. I hope they will share their stories and tell how they got help.