Hello!
My first advice would be to see a doctor about your back to see if there is a bigger underlying issue that you need to know.. BUT what you can do in the meantime is modify the jumps, or whatever is causing you pain, so that it doesn't hurt. Focus on landing softly and make sure your knees are slightly bent when you land so that your back doesn't get the full blow of your land. What kind of shoes are you wearing during this video? That could also be something to look into. Also, what kind of surface are you doing the plyometrics on? When I did Insanity in my garage I eventually HAD to get some mats to use otherwise my knees would be painful.
I hope some of this helped and gave you some things to think about

Let me know if you have other questions
Andrew