New position is a pain in the butt!

Have a new bike-Cervelo P3. Position is comfortable except there is an enormous stress on my butt muscles. On my old bike, a Felt B2, I had muscle stress in my lower hamstrings but now it’s upper hamstrings and it’s making my run miserable. I’m not sure if I should go up more, back or forward to get this stress off my butt.
Thanks for any suggestions

You should be more specific. Is it proximal hamstring, piriformis, or ischial tuberosity pain?

Thanks-It’s my whole butt. I’ve been doing tris for many years and this is the first time it’s happened to me. As I stated I usually stress the lower hamstrings-above my knee to lower butt