I'm not a teen, but this is something I can help you with.
Yes, your horse is sore through the back given the information you have provided. Please do not attempt to ride him until this is fixed.
The first thing you need to do is consult a chiropracter, and get this kicking sorted out. The kicking is quite likely a result of the back pain, which is now becoming worse from the kicking - a viscious cycle that needs to be broken. Is it possible to allow him to spell in a paddock for a few weeks?
At the same time as contacting a chiro, please also get onto a qualified saddle fitter. If your saddle is not 100% perfect on his back, it's going to cause soreness and no amount of chiropractor visits will relieve that.
From there, making sure ifs not you causing the issue as well. Avoid plonking down hard in the saddle, avoid bouncing in the saddle and so on. That will all contribute to back pain.
You will get more answers by having this thread in 'Horse Health' rather than the teen section. If you are happy for me to do so, I will move it to the appropriate location.