Baby choking! :(

Krystin
My daughter is 18 weeks old.  Since basically birth she has had these choking episodes where she chokes, it comes out of her nose, and she can't breathe and it scares the sh*t out of me and her. There has been times when I was ready to call 911.  She is diagnosed with acid reflux and takes Zantac for it, and has a milk protein allergy and is on Alimentum because of that.  It is certainly not as frequent as it used to be, but it still happens and is still VERY VERY scary.  Now that I have had to go back to work and will have other people watching her (family, all with baby experience), it is scaring me even more because I won't be there at certain times when it happens.  My grandmother just called saying that she just had an episode and that it was very scary.  She had an ultrasound at about 9 weeks old for Pyloric Stenosis and they said she didn't have it.  Her doctor insists that this is normal and that she will grow out of it.  I don't want to undermine her doctors, but it is concerning me.  Has this happened to anyone?  What could be causing this?  Will introducing cereal and baby food make it worse because it is thicker?  Is it possible that some kind of hole/ opening in her mouth/ nose area did not develop properly or something?  Should I bring her to a GI doctor?  Maybe I am overthinking, but I truly am scared. :(