You comment that some weeks are fine. What do the two of you do right during those times? During the bad times, what sets things off? What's the difference? One thing I've learned from a book called "divorce buster" is that the phrase try, try again does not apply. If you ask your wife how her day was and it turns into a fight, approach it differently....or maybe you don't ask at all. Maybe she tells you something, you try to provide a solution and then she starts getting mad. She may not be looking for a solution, maybe just an ear.
So far, I've gotten good advice on this site and from the book "divorce busters".