I look pregnant already at 4-5 weeks..?

This is my second pregnancy, I had a positive instantly 9 days before my missed period. It makes no sense. I assumed last month was spotting and that I was actually 8 weeks. But from the ultrasound yesterday it looks like we are around 4-5. Below on the left is right when I got my positive. The picture on the right would be about 4 weeks. This is so bizarre.. my last pregnancy it took until 15 weeks to show, but I also was 160 lbs. this pregnancy I’m starting at 125 lbs. I know the baby is way way too small to cause a bump. Has this happened to anyone else? I’m guessing it’s just from muscle memory/bloat/my uterus preparing?? It’s just such a drastic difference