I got a call the other day from a number I did not recognize and it didn't come up in the conventional reverse lookup directories.
I did put the area code and prefix into The Telephone Prefix Location Directory and found that the call was from a cell phone in Los Alamitos, CA. Not knowing anyone from that neck of the woods, I was able to continue with my day, secure in the knowledge that it was just a wrong number.
Of course, not everyone worries about this sort of thing. But, if you do, that site is for you.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.