Kit: Saddle Weary

Went up to Barrington River over the weekend for white water kayaking. 0.45m water level, grade 1-2 rapids. 17km in 7 hours on the first day - as a result of many beachings on top of rocks, and feeble struggles to get off them. 7km in 4 hours on the 2nd day. I have 'saddle sores' from sitting down for so long. Cannot believe how tired I was on Saturday night (I haven't been so in the past) - is 8.45 pm an acceptable time to go to bed?