First I would check the basic mechanics of the hitch and make sure nothing is off. Also, I would second making sure the tires are inflated to the proper pressure for the load they are bearing, not automatically the max sidewall pressure. This is especially true if you're running any tire capable of handling more than half of the GAWR.
Second, I would run it across a scale and compare the weights to my last known good setup. Maybe you changed how the trailer was loaded and simply didn't realize it. Don't have a last known good setup? Shame on you... $11 at the local CAT scale will highlight any issues with the weight distribution, and could show you exactly where the problem is. By the same token, it can eliminate the weight distribution (or lack thereof) from a possible cause of the problem.