What is causing my caravan to sway?

If the balance of the caravan is incorrect then it will sway

When it is swaying the caravin is actually going faster than the tow car and to correct it you first need to apply the brakes just on the caravan then slow down once the sway is under controll. You should then stop and re adjust the weight position on the van to stop this happening again.

The correct balance is a higher proportion of the caravan weight is toward the front of the van, if youadd to much weight to the rear of the van then the van will tend to sway, eg bikes plus water or fuel and a tool box on the rear bumper of the van will create this situation.

If your caravan weight is 2500 kg then your ball weight should be between 200 and 250 kg

This utube does a good job of explaining how sway occurs and how to safely resolve it.