I would crawl underneath and take a look at the spring hangers, the equalizer hangers and also check for a broken spring or bent axle. You may have hit a pothole or something that either bent or broke one of those items, or they could just be wearing out.
You would be amazed at the short time it takes to destroy the plastic bushings inside the spring eyes. Take a look at
this thread for some eye opening pictures of what they can look like.
If only one of the tires is wearing unusually, it kind of eliminates an overloading problem. I am not a tire expert but that is what I would do in this case and then I would take it to a good tire shop.
Good luck.
Barney