concerned ???

I'm 17 weeks 4 days pregnant and I took my daughter out for a walk on her stroller and I walked for about 45 minutes to the park but it was more like slow slow walk not like a fast walk but when I came home and rest after picking up my son from the bus stop I started to get like pain under my belly button and cramping and I was laying down and I couldn't even stretch my legs because it would start hurting it would even hurt if I would walk ...I told my husband about it and he asked me if I carried any heavy and I said no all I did was went for a walk and push the stroller ...has this happened to any of you guys ????