Hi C.. If you notice that she's acting different, she could be dehydrated. After she vomits, try to give her a little bit of water or pedialyte to replenish her fluids. You can use a baby medicine dropper and just give her a little bit at a time. Dehydration is very dangerous and you need to watch her closely if she is vomiting and make sure she drinks some fluids more often than usual (just a little bit at a time, so she can keep them down).
Are you breastfeeding? If so, keep a journal of what you have been eating and drinking and see if she is vomiting from a specific type of food/drink from you.
If you are giving her formula, she might be having a reaction to that type of formula. You might need to try a specific kind of formula that is gentler on the tummy (which should help if she also has acid reflux which is causing her milk to come back up). They have lots of special kinds of formula for that these days. My son was on Alimentum (made by Similac) for severe acid reflux that we finally figured out (when he was 3 months old) was what was causing him pain from a milk intolerance from birth.
By vomit do you mean spit-up? Because spitting up (just a little bit of milk comes back up when you burp her or something) is pretty common with newborns/babies. Is she fully vomiting (forceful, big amount)? Because that could be part of a milk intolerance.
The only other thing I can think of for her to react in a different way (by not following your voice/noise...) is that her hearing was somehow temporarily affected by her vomiting.
Definitely keep an eye on her.
You can usually tell a milk allergy by abnormal (painful) crying, vomiting/diarrhea, gassy/fussiness, extremely loose or abnormal stools, rash on the body.
Good luck. My son is my first too - and it's hard and scary trying to figure it all out.