That major soreness pain is totally normal. It's a good sign that your weight is pressing right where it should be.
My first couple of rides every Spring produce this same sitbone pain- really painful!, especially the first couple minute sin the saddle- but this soreness fades over a few more rides. Give your sitbones a day or two of recovery in between long rides and build up the distance in increments.
Itis incredibly paionful sometimes- but it goes away!