OK, in eleven days you've done 161 miles, but your total mileage for the year is only 725. So that implies that you have recently increased your mileage quite dramatically, given that in the first six months of the year you'd done less than 600 in total. Why would you be surprised that this results in fatigue? You need to adjust to a higher mileage load. In my view the number of days on which you are cycling is very much a secondary consideration.