Ok, then it sounds like you have a sway problem. Usually in these cases people get a little bobble from the road conditions or a push-pull from a passing vehicle, so the trailer "sways" over and back. *A* sway is not "trailer sway."
If it's oscillating and you need to apply trailer brakes, you've got a problem.
Most likely it's been a problem for a while, which was masked by the sway control device. It's now gotten to the point where it is overcoming the sway control device, which is not good.
Take an inventory of what's in the trailer, especially what's behind the axles. You may think nothing has changed, but over time you slowly add-add-add, not really thinking about where you put things, and over time, it adds up. You may find several hundred pounds of unnecessary "stuff" in the rear storage compartments causing your sway problem.