If its your first then very normal to not feel any movement yet. With my first I was over 25 weeks before I felt anything and nearly 30 before I started showing. Seem to be the complete opposite this time round!! :-) you'll feel baby soon x
Yes it sounds normal, I didn't even a big tummy till around 26 weeks, don't worry, if the doctor isn't concerned you shouldn't be, best of luck
We all grow at our own speed. We all carry slightly differently as well. Your OB will start measuring your tummy, and is also monitoring your weight. Trust me when I say that they will let you know if there is any problem. Doesn't sound like there is anything to be concerned about at all. Congrats on your pregnancy!