Cardio and Cramping

Before pregnancy I always jogged as my cardio. I would run for up to an hour. Since pregnancy, I have been slowing down, taking more walking breaks, and had a good system of switching between walking and slow jogging for 20 min. Now I am 22 weeks and even when I just go for a walk I am feeling side cramps. I'm worried if I push through cramps that is hurting my baby, but I want to keep up good cardiovascular health to help me through labor and delivery. Has anyone else experienced this? Any suggestions?