Three weeks and pants are already too tight!

I'm exactly three weeks today, and I went to put on my favorite pair of shorts and it feels like I'm suffocating. On my tummy where they're usually flat, it sticks out like a little foothill. This is my first baby, but I'm also quite small. My waist is usually a double zero and my hips are anywhere from a 0-4 depending on the pants. Is there something wrong? Is it just bloat? Is this normal? Could really use some advice to ease my mind !