Weight gain

I’m 35 weeks now and I’ve been at 17lbs gained for a month now. My stomach is SO big and getting bigger but I’m not gaining weight and I’m so confused. Is this happening to anyone else? My last pregnancy my bump was so tiny (I had a girl, this time it’s a boy) and I gained 20-23 lbs but it made sense because my bump was tiny.

Plus I have a stretch mark now on my tummy...that’s how big my bump is😭

Want to add I started out at a healthy weight so I’m not overweight at all