+1
You didn't build up your endurance is how I see it. I give you credit, you can knock out 20-40 miles but 90 mile days in the saddle is way different. You have to build up for that. Before I did a double century, I made sure I could handle 100-125 miles with ease. Anyway, next time, just build up to it and you'll be ok.
Or sometimes doing long distance training rides will show up any bio-mechanical problems like wrong saddle or shoes that training won't fix.