My 9 year old schnauzer is pulling her neck up

[Starrfire100]

She starting having issues with eating her food so the vet extracted 9 bad teeth but after she recovered she was still having issues eating took her back to the vet they did blood work it came back normal she was throwing up this yellowish white foam so they did a urinary test it came back neg .. then they did a X-ray and told me
She had a tumor in her stomach but then when opened her up there was nothing ..he checked everything and all was ok .. after she recovered she started pulling her neck up and gagging which after some research I thought it was a reverse sneeze or a collapsed treacia the vet gave her a low dosage steroid she has been on this for about a week and there is no change .. the neck pulling and this gagging continues when she finally gets comfortable she starts to yelp .. we are at a loss for what is going on .. please help me