if you rubbed the skin down badly on the 1st ride, then it's likely gonna take a longer time for it to be less tender and less susceptible to further damage. Your's sounds really nasty.
Long rides in wet conditions are tough.
I guess you could call it saddle sores - but usually I think of infected hair folicles, sweat glands and such.
Strictly from personal experience I found a good snug/tight fit with really thin chamois works the best for me in wet conditions. This may be different with some of the newer chamois designs - wouldn;t know since I've not tried them all. I've done quite a few very hard rides over 100+ in varying states of rain, and not had much more than really cold privates. Course you gotta treat it all a little better after that kinda ridin.
Ideally the chamois pad should retain a minimum of moisture and not allow fabric movement.
were the shorts you have Gel padded? gel shorts may be the single worst thing ever in cycling kit.