Yes, pregnancy bloat. At 4 weeks pregnant your uterus has not changed enough to cause any protrusion from your stomach. You are going to notice your boobs grow faster than your stomach at this point.
Due to hormone changes, etc, you get really gassy, there is more fluid build up and a lot of women get constipated during early pregnancy. ALL these cause the dreaded pregnancy bloat. Which is totally normal and expected.
Most pregnancies don't truly start showing until the uterus has grown above the pubic bone. That will be around 12 weeks. First time pregnancies show later - I've known women who don't start showing until they are 20 weeks.