stomach problems?

I already talked to my doctor about this but my current doctor sucks so I’m just looking to see if this has happened to any other babies until I get a new doctor in a couple weeks.

My son is 9 months old. He throws up after he eats almost every single time, mostly formula. He always wants to eat, and he doesn’t seem fussy. His poop is normal, sometimes it’s a little loose. So I mentioned it to his doctor today and then they weighed him and he’s lost weight since he’s been 6 months old! So now their kind of concerned. Their sending me to the children’s hospital for a test but other than that he has no idea what’s going on. Has this happened to anyone’s baby before?