Agree with sfa... stress and anxiety can do funny things and sounds like your first ride was a bit stressful! You can hold yourself in a tense manner or in a weird position and cause all sorts of weird aches and pains. Ride somewhere familiar to start, keep yourself as relaxed as possible.

A sore butt/sit bones is normal for a while, but a seat that hurts your soft tissue probably always will. I have found that heavier padding on seats hurt me more than a firm seat, but that isn't necessarily true for everyone.