30 miles is a short ride except at the end of a 1000k, where it seems like forever. I misread the cue sheet and thought I was almost to the end of my ride Sunday morning. Then I realized I had somehow missed the 8 miles between turns. I was prepared to be upset, but I had plenty of time and it was nice out.
I remember once when I had been studying too much and stopped riding. I went out and rode 5 miles and it was a big effort. Ride whatever is comfortable to you and then try a little more. But yes, get at least a rudimentary fitting. Sounds like your saddle is too low.