Working out?

Okay so i am 17 weeks and today i started working out again since i became pregnant and i just got on the treadmill and not running or anything just fast walking, and i start getting pressure where my uterus is, and stabbing pains in the vagina that only lasted for couple seconds, now i got some stabbing feeling lower stomach but not painfull. Is this normal while working out, i use to work out but stopped at the begging of my pregnancy and its scary but i want to. Be able to work out but now i am sitting here and scared.