6 week old strange reaction

It’s happened twice now and it’s hard to explain, but I’ll try my best. I’ll feed my daughter and about an hour later she’ll start to fall asleep. Well, while falling asleep, she randomly jerks and starts SCREAMING bloody murder. Her eyes get super watery immediately, and it’s not tears because she just starts crying, and she gets bubbles forming on her mouth and inside her cheeks from formula. She hiccups a little afterward. Could it be a hiccup that hurt? That’s the only thing I can think of. She just switched from breast milk to formula also.