No protruding belly at 3 months, is this normal?

Yes. Everyone carries differently. At three months the uterus is not big enough to protrude into the abdomen for most women.
Yes. Not having a belly 12 weeks is very common. Everyone's body is different and is dependent on if you have had a baby already, your weight and general physical condition. I find that many women are worried because of other people's comments. Such as " are you sure you are 3 months, you look small". If there is a concern about your size at any time, discuss it with your doctor.