Have this checked out and if you do need to put a shim in your shoe you might have just found out the secret insiders have known but won't tell you because they want you to be a regular customer of health services in relation to this. And those health services can add up to be very expensive over time.
Sometimes just having a mature family member look at your posture can tell you if it is likely to be true. Have you tried all other sorts of health treatments? I myself am considering cutting a piece of leather to put under the insert of one of my shoes; most likely my right one. In fact I will do that.
In fact if you think insightfully and conceptually about it; one leg being shorter than the other would indeed create a low pressure spot on one side of a spinal disk whereby it could bulge or slip out of.
Sometimes the shim is only one eighth of an inch thick?
In retrospect it should be the first thing that they look for at any place that treats lower back
And it is indeed one of those things no one would want to believe about themselves as being true if you told it to them. So indeed it would be an easy secret to keep!