Could be bloating/fluid retention and it may actually go down again soon! Every body is different though and if you are showing already then that's not unheard of either. :) your abdominal wall is generally not as strong after baby #1 so doesn't hold things in as well but the uterus at 6 weeks is still well down in the pelvis so it's less likely your bump and more likely just fluid that will ease :)
They say it's because your uterus never had time to fully shrink back down before getting pregnant so it's just faster showing since your body just had a baby in there 😅