It sounds to me as though it is part normal and part saddle.
It is going to hurt for a while when you start out and you are correct, the extra weight doesn't help. Start with shorter rides until your butt gets used to it.
Make sure the saddle is the correct width for your sit bones.
It also sounds like the nose of the saddle may be a little high. Try tipping it down it 1/8-1/4 inch.
Nothing you do will bring immediate relief, your body has to get used to the new form of abuse!
