Why would my testicles hurt and my lower back ?

Pulled muscle: If a muscle injury in your low back is causing the back pain the nerve that runs through that area innervating your scrotum could be affected as well.

Get checked: Conditions which come to mind include prostatitis, epididymitis, and the passage of kidney stones. There can be several inflammatory conditions which can cause your symptoms. Please see a doctor rather than relying on this on- line format for a proper evaluation.