I don't see ahything wrong here. It could be that you're experiencing the prblem that many do - as the muscle bellies of the sinal erectors grow (stress -> recovery -> adaptation (larger muscle), the fasacia that surround them can't keep up. This tends to cause a dull ache, and it's going to be around for a while until the faascia has time to expand.
What I *don't * like is your tendency to bounce the bar around on your back. Don't do that. Your back wil thank me when you're 45. Look up "impact loading" to understand.