If you haven't been riding in awhile, EVERY seat is gonna be a killer.
You need to build some butt cauloses. Instead of a long ride every weekend, go out every night and ride around the neighborhood for about 20-30 mins. You'll have "cheeks of steel" in no time.
L8R
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger