I'm 33 weeks pregnant, 3cm dilated, 2 previous premature babies, and I'm having constant lower back pains with sharp shooting lower back pains every 5-7 minutes should I be concerned

Have you called your OB/GYN? If not, I'd get checked out at the hospital you're scheduled to deliver at.

Talk to your OB/GYN to figure out what is going on. You can be dilated a few cm for a few weeks before you give birth it could also be a sign, with the pain, that something is starting. If you can get a quick OB appointment go to your hospital to the triage.