Yeah, I really think you'd be best off re approaching your training from one step down. So not as an intermediate but as a beginner again. You need more reps, more practice and now this is a perfect time for you to build up your lower back so you can finally solve the lower back issues which have riddled your training (yes I do pay attention to the people I moan at).
So basing this off the premise you're training as a beginner again. If you look at this article here:
Training Frequency and Muscle Building: Huge Gainer Round Table #1 | Muscle and Brawn Bodybuilding, Powerlifting and Muscle Building.
You'll see that it's a popular opinion, train frequently with a small pool of exercises. This is your opportunity to go back and fill in bits of your foundation which were never there in the first place, as is evident with all of your major lifts.
3 x 3 won't cut it either. You need dedicated lower back work for medium-high reps. If you can't do either the squat, bench or deadlift three times a week for moderate volume without pain, then you are a prime candidate for remedial work.
You are just that.