fetal movement or pressure?

Ugh! I don't know what I'm suppose to be feeling. I am exactly 19 weeks pregnant today with my first baby. I keep reading that fetal movement is first felt between 18 and 20 weeks (typically) and feels like bubbles, gas, butterflies, popcorn, blah, blah, blah. What I have been feeling– about 4 times now… is almost like a pressure in my uterus that last a couple seconds and feels almost like a rolling motion. I guess my question is- could this be fetal movement? I don't know because I've had so many sensations in my abdomen that I attritbute to the expanding of the uterus (twinges, pulls, stretching) that I don't know if this may be the baby moving or just growing pains. Has anyone else had this? Thanks! =)