blow, elcrux's comments touch on the myriad of things that can be factors, and touches on the importance, or specifically, the advantage of riding regularly and becoming more attuned to the details--no different than any activity.
when I think back 20 years or whatever, I never really gave much thought to a seat or bike shorts, whether it worked or not.
I guess just part of finding improvements is good old trial and error, but it certainly helps the more often one rides and rides regularly to help figure out some of the small details of where discomfort is coming from.
and yes, supported trips are a great way to start, although 110km 70mile days are nothing to sneeze at, especially if hilly, and a lot more seat time than most riding that we do recreationally, a lot more time to show up small fit or equipment or clothing issues that become bigger issues as you and most of us have experienced at some time.