almost 15 weeks and not showing at all?

I'm not sure if this is common or not, but I'm almost 15 weeks and not showing at all :( I'm just a bit worried because I had a few complications early on in my pregnancy, that did clear up, but I haven't had an ultrasound since 8 weeks and just want to know my baby is there. this is my first pregnancy, and I only weigh about 110lbs. (I've gained about 5 pounds!) just wondering if this is normal and when you ladies started to show?