not to say it cant be, but it most likely is bowel distention from gas and
bloating, constipation. you also get a bigger tummy earlier your next time around, but 4 weeks is too soon to be from baby. i am 6 weeks with baby #3 and im huge! was last time too, then all of a sudden my bloating went down and i looked a bit normal again. keep us informed, let us know if there are more in there!
(because my tummy looks so huge right now family is calling me octomom, nice huh?