4th pregnancy, twins

I have 3 boys and im currently 9 weeks and 3 days pregnant with twins. I have read how people are already starting to show but i haven't noticed any change in my stomach size nor weight. I only gained two pounds so far this go around. Should I be worried? At the most I've noticed my hips, thighs and butt is spreading but not my stomach. Any advice to what's going on?