spitting up/throwing up

It's been about a month since the first time one of my twin daughters threw up. We thought it was a bug but nobody else got sick except for my second oldest daughter a couple of days later. But anyways, in the past month she has thrown up/spit up like four or five times. The first time, she threw up a lot within a few hours. The next time it happened was like a week ago and she threw up in her bed. Yesterday and today, i noticed something coming out of her mouth. It was chunky like spoiled milk, even smelled like spoiled milk and it wasn't a lot. I don't know if it's normal or if it's something to talk to her doctor about.

O and her "spit up" (spoiled milk smelling one) is weird because she doesn't feel hot and she is normal. I don't know what is going on with my child but I'm starting to get a little worried. Just don't wanna question it if it's nothing to worry about. TIA!