The only thing I've heard from 2 other twins expectant moms, and it happened to me as well is that when you do the pharmacy test the 2 likes show right away, one you pee on the stick, they're there...and lots of morning sickness.
As my daughter checks her temperature haha, I'm hoping that's what it is. I read around that it's common for things to feel more emphasized but wasn't sure how early I can feel it.
I was bloated a lot during my first trimester-I had to start taking fiber tablets to help keep me regular and reduce gas pressure
It could be pelvic pain from everything being stretched from your first baby. I have this and have just been fitted with a belly brace which has helped a lot.