Ay, normal lang yan! Every pregnancy is different, ang iba mababa talaga ang tiyan kahit kailan, lalo na kung first time mo or kung maliit lang ang baby, kaya hindi ka mag-alala. A few of my mom friends din nag-worry about this, pero ang OB nila sinabi na basta healthy ang baby on ultrasound, okay na. I'd suggest mag-check sa OB mo just to be sure, pero most likely walang problema, basta naka-monitor ka lang regularly.