Lately, my testicles have been very tender. I have no idea why really. (I'm 17 btw). Is this normal? (Since this has been happening my back also hurts more). They both seem a little bit bigger to me also. Ask if you need more info.
It can happen occasionally, but if it continues for more than a day, or if the pain becomes strong, you should get to a doctor. If the pain is severe you should get to a doctor or ER immediately as it could be a torsion, which requires emergency treatment if the testicle is to be saved.
With the back pain as well, it sounds like something is causing inflammation. You definitely should see a doctor.