You've sad that a couple times now But you continue to hang stuff out back on the dropped gate. On a short trailer like you have with the bulk of the payload area behind the axle, it isn't going to take much for the tail to start wagging the dog. First place you should start loading in your situation is that that tongue box, and don't be afraid to load it heavy, and then load your heaviest junk as far froward in your trailer as you can get t. Better to be heavy on the tongue than light, especially something that short.
I know folks like using truck beds as trailers because they think it's a cheap easy way to go and it "matches", but some are more suited to that task than others and honestly, the proportions on your bed are about 180 deg out. Without additional work you're going to have to be really on the ball with how you load.