No two women are the same, and babies are also different. Baby bumps develop at different times for everyone, and there is no way in which you can tell in advance how your pregnancy bump is going to develop. As a rule, first time mothers take longer to start showing than their "sisters" who have already been through one or more pregnancies. Still, most mothers will have a baby bump by some time during the second trimester. Don't worry if you are already in maternity clothes at eight weeks gestation, or if you are still not showing late during your second trimester. Your shape and size in pregnancy mostly depends on your pre-pregnancy shape, and has a lot to do with your muscles, your size, and how tall you are.
If other people are constantly telling you that you are too big or too small for the length of your pregnancy, you are not alone it seems like pregnancy just does something to people that makes them want to make horrible, nosey comments. Tell them your doctor says you are fine, and they will probably stop commenting. The speed at which you are growing can sometimes tell you something about your pregnancy though, which is why prenatal care is so important. Women who gain weight extremely fast could be carrying twins or have gestational diabetes, while those who are not growing at all could face developmental problems with their fetus. But just your size should not lead you to premature conclusions all of these things can be easily diagnosed by your healthcare provider.