FTM so I'm not completely sure if this is Braxton hicks...lately i've noticed that when I walk for 20 minutes or more, my stomach/uterus gets really tight and uncomfortable (almost like cramps) and knocks the breath out of me. It's constant the entire time I'm walking for longer periods of time such as grocery shopping or walking around the mall. About 5-10 minutes after I sit and rest, they go away.