Braxton hicks/tightening stomach after walking 4/5 weeks pregnant

Heaven

You read right. I just found out I’m pregnant with my 5th pregnancy (2 living) and I regularly lift weights and do light walking on the treadmill after. I’m only 4.5 weeks and already feel the tightening in my lower stomach. Is this normal after having so many pregnancies or am I crazy?? I know some things happen sooner the more experienced your body is. 🤣