Belly cramps while walking?

Camille • ♥️ IVF baby 03/2021 • Miracle baby 11/2017 ♥️

I'm 29 weeks. Early on my doctor suggested taking 30 min walks every day to stay active since I have a desk job and don't work out very often, but lately after walking for 15-20 mins I start to get a really bad cramp in my lower abdomen, in the bottom/underside of my bump. It hurt so badly I was almost in tears after grocery shopping today.

Is anyone else getting this? It feels better almost instantly if I just sit down for a little bit.