Pls help- Dog vomitting and barely eating for the past 4 months

We have a 10 year old Chow/Retreiver mix who has always been a picky eater.  Lately though, she'll go for days without eating, and she then vomits white foam or yellow liquid,...sometimes it's chunky and looks like it has specks of blood in it.  She's also been having diahrea and has not been able to control her bowel movements in the house.  She's lost a lot of weight, but somehow still seems to have energy and otherwise behaves normally.  We took her to the vet, had blood tests and x-rays done and it all looks fine.  The vet gave us meds to increase her appetite and to reduce nausea, and we've been giving her pepcid.  Nothing has helped.  He can't figure out what is wrong and the only thing he can think of to do is a sonogram.  But there is no guarantee that he'll be able to tell us anything from the sonogram, and it's another $400 that we'd have to scrounge up.  If I knew that the sonogram would give us some answers, I'd do it in a heartbeat.  But I thought the x-rays would have and they showed nothing.  Does anyone have any advice?  Would the sonogram help?  Any ideas on what could be going on with her?  Help please, I don't want her to suffer and I'm getting tired of cleaning up vomit and poop all day!

[ginger899]

Has your vet run full bloodwork? To check liver values/kidney/pancreas, etc?
Sonography is very different to Xrays. They take high definition scans of organs. Imagine seeing an ultrasound of a baby in the womb....now imagine trying to see the same definition by X rays. It wouldn't be anything like the same detail.

Sonography can detect tumors in organs (Let's hope that you dog does NOT have a tumor...but it is wise to find out) -and will show up things that X rays can't.

I had an ovarian tumor once. It was benign, thankfully, and I had it removed. However it had to be diagnosed by ultrasound, not by X ray.

[Margot49]

I think I would definitely have an ultrasound done.  Not all Vets have this equipment and not all Vets are trained in reading them.  I'm sure they can see the obvious but an expert goes through about 4 years of training, I think, to qualify to be able to interpret an ultrasound.  I don't  live in a large Metro area. There are at least 2 Vets here that have ultrasound equipment but they have one of two certified doctors come here to read the ultrasounds.