You are a little young for this but you most likely have a dysplastic or degenerative spondylolisthesis at L5-S1. See https://neckandback.com/conditions/degenerative-spondylolisthesis-or-spondlylolysthesis/
This is generally not a dangerous condition but with continued compression of the nerve roots, this could possibly lead to some root injury. The next step is an epidural steroid injection (ESI) to try and calm down the nerve roots.
Pregnancy can exacerbate this condition as the added weight, change in spine biomechanics and secretion of the hormone relaxin which allows the ligaments to stretch somewhat can increase stress on this level. You can more likely than not carry the baby to term but might need some treatment along the way.
Dr. Corenman