Assuming nothing is bent (including steering components), and your front is is properly aligned then it’s probably weight distribution side to side. Have you scaled it yet? If not, start there and you’ll have a good idea of what to change.
If you don’t have access to good scale setup, then just invest in a set of cheap bathroom scales. They work fine as long as you are careful and can repeat the scaling the same way each time. (well, that goes for a good scale setup too).
BTW: I remember reading somewhere you can scale with just one or 2 scales. Maybe someone can chime in on that procedure….