Scott,
Do you mean you have excessive negative camber on the o/s rear wheel (UK drivers side)? e.g. the wheel leans in to the car at the top.
Or do you mean the wheel is wobbling e.g. buckled?
If it's the former of these two then this isn't unusual as long as the other side is doing the same (check on flat ground). If you still think this is
too much then it is likely that you rear spring is in need of replacement/refurbishment.
If it's just the one side then this could be one of a number of things... twisted anti-roll bar, tired front springs, worn dampers, heavy driver

.
If the wheel is buckled then you either need to get it straightened or replaced. You should also check the drive shaft for buckling/cracks as that is
very dangerous. Also, check the rear brake drum for cracks too as it may not actually be the wheel that is the problem.