, I'd have it checked out now
. Honestly. Back injuries are nothing to mess with. Things that happen when you are young can seriously impact you when you get older. You need to know what you did and how serious it is. Try to see a sports physician, if you can.
I agree with Jen--this isn't likely to have anything to do with P1. The reason she mentioned is exactly right. Usually people are far too tired to increase their workouts in P1. But it shouldn't lead to injuries.
Before you start exercising again, check with the chicks in the exercise forum
(there are some really smart people there!), look at the videos on how to do exercises on YouTube, and/or read about how to correctly do exercises online, okay? Especially with things like squats, it's really important to do them correctly or you may hurt yourself.
One good rule of thumb is that any time you raise your arms above your shoulders, suck in your stomach to protect your back.
Hope you feel better soon!