Only 3 Days? I also have only been riding three days and my butt hurts. It just takes time in the Saddle to get your glutes used to the ride; however, a good seat also helps. My current bike has a Bontrager Saddle but I recently ordered a Fizik Arione because I have heard it is a great saddle.
First Day: Rode 16 miles, my butt hurt the whole way.
Second Day: 20 miles, my butt did not really hurt until about the 10 mile mark.
Third Day: 24 miles, my butt did not really hurt until I hit about the 13 mile mark.
For me, once it starts hurting, it hurts bad. I am chalking it up as a bad saddle and being new to the bike. I cannot wait until my Arione gets delivered but in the meantime, I just suck it up and ride. I need to increase my endurance because I have not exercised in over 2 years. I have been a complete couch potato..