Without wishing to antagonise the
flamers amongst you all, if he has decided to quit then let him quit.
Although there has been a lot of sense entered into this thread by many people, David is clearly unsure about whether he wishes to continue learning.
If it is purely a clash of personality with an instructor then he will change instructors (IF HE REALLY WANTS TO CONTINUE WITH IT). And if he REALLY wants to continue he will change instructors ten times if needs be to achieve the final goal.
No offense David but the decision is black and white. Whirlybirds advice was spot on........there are good days and there are bad days. If you have 3 bad days in a row you forget about the good days and what they feel like.
I would suggest you get back in the seat for one more hour and go for it. If it is still hellish tell the instructor to be honest with you. He might even say you aren't up to it, he might say you'll be qualified in a month. Unless you ask you won't know.
Sorry to be blunt but that's moi!