Golden retriever burps a lot and now vomited today?

So we adopted a 5 year old golden retriever 3 weeks ago, she burps a lot I've noticed and burps loud, especially after she eats. woke up this morning to 4 piles of vomit 2 she ate 2 still looked like regurgitated food. Then while at work hubby said she puked but before he found it she ate it again, and then later tonight she puked greenish liquid (bile?) with a little white mucous no blood. she has been a little sad other than that breathing normal, and she took a piece of plain chicken from me no problem . Her stool has been fine her food has not been changed from the previous owner who told me that she does best on pedigree and not high end food because it upsets her tummy, she also told be that the burping the vet said to mix wet food with her dry which I didn't know and have been feeding her dry food and to put an alka seltzer in her water .....I will get up and feed her a cup of food and she usually doesn't touch it till later, oh and she's been drinking water normal, taking her to the vet tomorrow, what could this be?,