Why vary from week to week?
Stick with a program and give it a chance to work.
You're not falling for the "Keep The Muscles Guessing" broscience are you?
I vary my majors, and while i say 'varies week to week', it realistically varies every couple of months. I find that I tend to plateau very quickly if I maintain the same workout schedule for longer than about 6 weeks, to i'll generally rotate my three major muscles through three major exercises each week to help with gains. Two of the guys that I have gotten a lot of knowledge from (the guy who trained James Potter and a local natural BB champ) agree with rotating the three majors through a couple of different exercises to contantly push for better gains.
So i'll usually pick a the four or five minor exercises that I do for each major muscle and stick to them for a month or so, but rotate my major every week.
So for back it might go
Week 1
Pull exercise to front - A
Dead from standing on a platform (for maximum depth - bar just touching feet)
Row Exercise - A
Pull exercise to rear - A
Flyes to rear - A
Week 2
Pull exercise to front - A
Deads from the floor
Row Exercise - A
Pull exercise to rear - A
Flyes to rear - A
Week 3
Pull exercise to front - A
Rack Pulls
Row Exercise - A
Pull exercise to rear - A
Flyes to rear - A
Week 4
Pull exercise to front - A
Dead from standing on a platform (for maximum depth - bar just touching feet)
Row Exercise - A
Pull exercise to rear - A
Flyes to rear - A
Week 5
Pull exercise to front - A
Deads from the floor
Row Exercise - A
Pull exercise to rear - A
Flyes to rear - A
Week 6
Pull exercise to front - A
Rack Pulls
Row Exercise - A
Pull exercise to rear - A
Flyes to rear - A
NEW CYCLE
Week 1
Pull exercise to front - B
Dead from standing on a platform (for maximum depth - bar just touching feet)
Row Exercise - B
Pull exercise to rear - B
Flyes to rear - B
Week 2
Pull exercise to front - B
Deads from the floor
Row Exercise - B
Pull exercise to rear - B
Flyes to rear - B
Week 3
Pull exercise to front - B
Rack Pulls
Row Exercise - B
Pull exercise to rear - B
Flyes to rear - B
Week 4
Pull exercise to front - B
Dead from standing on a platform (for maximum depth - bar just touching feet)
Row Exercise - B
Pull exercise to rear - B
Flyes to rear - B
Week 5
Pull exercise to front - B
Deads from the floor
Row Exercise - B
Pull exercise to rear - B
Flyes to rear - B
Week 6
Pull exercise to front - B
Rack Pulls
Row Exercise - B
Pull exercise to rear - B
Flyes to rear - B
The advantage of rotating the three major exercises like this is that it get easier each week, and you'll pull more and more. While it recruits less core, less back extensor - less everything - each week, I find that I can add at least 2.5kg on every lift every three sessions (so each time you do the lift). I've only been cycling like that for about three months, and i've gone from 140kg deads to 160 deads.
I do the same thing with my squats (but less structured in the order of those primaries) and have gone from 130kg to 160kg in about the same time.
Good enough justification :-D