My teammates and I call that "TT butt" (time trial butt). It occurs most often after a TT, obviously, because of the amount of effort involved and fighting to stay in an aero position. It also hits badly after a very difficult race where you feel like you're on the rivet and down in the drops or riding aggressively a lot of the time (even if you feel pretty good overall). It can definitely help to add some race-intensity training. Stretching the glutes, hamstrings, and hip flexors really well after a race can also help. I am personally a fan of cranking up the seat heaters in my car on the way home too .

The fact that your calves were cramping is another factor for your overall muscle pain. Keep hydrated (with water and electrolytes), and you'll have less dehydration related cramping. You can still get overexertion cramping, but sometimes that's not as debilitating.