Originally Posted by Kapusta

Pressured can vary a lot for a given rider weight based on the frame and shock in question, but 100psi does sound way too low for your weight on any modern bike.

Did you just aquire this bike used? If so, and this shock is 9 years old, it may be in dire need of a servicing if it never had one before.

What shock is this (brand and model)?

Can I assume you have already disengaged any lockout or stiff pro-pedal setting, if present?

When you lower the pressure enough so that you can compress the rear suspension, is it smooth? Or does it feel like it needs to break free from some sticky-ness?