Hey floss,
Please dont stress about what everyone is saying. You look perfect for 16 weeks. Everyone carries their babys differently and it also depends how many babies you have had. First bubs dont tend to show until a little bit later and subsequent babies pop out alot earlier. It all depends on your stomach muscles. If you have had scans and your baby is growing according to his/her age, then there is absolutely nothing to worry about. When I was training, I met this girl who was 20 weeks and still had a 6 pac!!!

In regards to the pain, it is most likely your muscles and ligaments stretching and making room for bubby. When bub moves or you move suddenly, they can feel a bit like a stabbing pain, and feel reassured that every mother worries about it!!. It can be a really odd feeling.

Hope that helps