Hi - Is the back pain you experience currently the same as the initial pain 6 months ago? What was the exercise that hurt you in the first place?
You could try dropping a set of 10 reps and see if you feel any different later. If it is better later then start there and slowly progress sets, reps and add other exercises. If not any better then consider holding off on resistance exercise and do more cardio.
As an aside I wouldn't get too worked up over your posture and muscle imbalance. The evidence is a bit murky as far as poor posture causing pain or good posture relieving pain. Just keep moving, eat healthy, get full sleep cycles and decrease stress!