Look on the driver's side door jamb for the sticker that lists cargo and passenger weight. Report back, you are probably overloaded.
Other things that can effect sway---Lack of weight distributing hitch or no provision for sway control installed. Weight of tongue is not correct, maybe influenced by loaded weight of stored items in back of trailer. Tires not inflated correctly. Soft tires or suspension on towing vehicle.
THat trailer is 30' long and it may be a case of the tail wagging the dog. Tell us what WDH and sway control you have installed.
