Same here...everone body is different.im almost 7 nd my shorts dnt zip neither tack anymore and ppl can alrdy tell
I understand, because I'm 7 weeks and people can already tell, this is my second baby, I didn't gain any weight with my first but I was 18 then so my body is really do some strange things with this one, lol!
Use a rubber band to button the pants or get a belly band. This early it is just bloating. I switched to maternity pants at 15 weeks because nothing fit anymore but wasnt noticeably showing until 19 weeks
It's most likely from bloating so drink lots of water and cut sodium : )