Bassnbug could be on the right trail but if it were out a lot it would wear the opposite side of the tire on the other side.
You could have a bent axle. The bend could be either from the middle out or could be from the spring perch out toward the end of the spindle.
In the old days when we ran straight axle race cars, (Yep I know, that had to be a long time ago, emoLaugh ) we attached a good chain at each end of the axle with a hydrolic jack at the
bent area and pumped the jack up 'till it was just past straight then let it off.
Measure from the ball hitch to the end of the spindle where you put the nut on. Lots of trouble but less expensive than a new axle.
Please be advised that this is DANGEROUS! You need to be sure that you have the chain hooked really good and some means to be sure that the jack won't slip off the axle and come out and KILL you, emoAngry Pay attention to what you are doing if you are going to try this. I know it works 'cause I've straightened several! emoSmile