Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your girl has been suffering from loud, wheezing, gasping episodes, with belly flinching like dry heaving. This sounds like episodes of reverse sneezing.
Do your girl's episodes look like the dog in the video in the link below?
I understand that she is also lethargic and eating poorly as well as vomiting much of what she does eat.
Reverse sneezing episodes can be secondary to inhaled irritants and how sensitive she is to them. They can be related to respiratory infections. They can be related to gastroesophageal reflux, excitement or post nasal drip or an overlong soft palate. Sometimes dogs will inhale a piece of plant material and until it dislodges they will have episodes.
In most cases these episodes can be stopped by rubbing her throat and getting her to swallow, so I would try that maneuver as soon as she starts. While these episodes aren't harmful in and of themselves as it's just a spasm of the muscles around the pharynx because of the irritant, it's no fun to watch and in her case it sounds like they are interfering with her quality of life because she is having several. It also sounds like they are linked to her vomiting and are likely related to gastroesophageal reflux and the irritation the acid causes her esophagus/pharynx.
If it is because of gastroesophageal reflux then using Pepcid-ac (famotidine) may help. Give her either:
1) Pepcid-ac (or generic famotidine) at a dose of 0.25mg to 0.5mg per pound of body weight orally every 12 hours for 2 to 3 weeks. That's one quarter of a 10mg tablet per 5 to 10 pound dog every 12 hours.
2) Prilosec (omeprazole) at a dose of one quarter of a 20mg tablet per 10 to 20 pounds of body weight every 24 hours.
If either of these helps she can stay on it as needed as acid reducers are relatively safe.
Reflux tends to happen more when dogs are laying down and sleeping as the gastroesophageal sphincter relaxes and acid can passively reflux up into the esophagus and pharynx. This irritant only causes more tissue swelling, thus dogs with reflux will also snore more. It may help her to get her to sleep with her head raised.
To ease stomach upset you can also feed a homemade diet of 1/3 boiled hamburger or white, skinless chicken, all fats and juices drained off the meat, and 2/3 white rice.
Sometimes reverse sneezing can be related to dental or gum disease and the secondary inflammation from chronic infections. If this is the case a good cleaning should improve things tremendously.
Rarely this can be related to an inner ear infection and the effects of the infection dripping down her throat.
Another rare cause would be a pharyngeal or laryngeal polyp or tumor.
Sometimes we need to sedate them and take dental radiographs and examine the pharynx and up behind the soft palate to find the cause, so that is always an option if this is worsening for her.
My concern for her however at her age, and given that she is lethargic and vomiting most of what she eats, is that there is something more serious going on causing her to reflux frequently. Metabolic organ failure (kidney or liver disease) or an abdominal mass putting pressure on her stomach are possible causes for her symptoms. If she is not spayed a uterine infection called a pyometra is also a possible cause. I highly recommend that she see her veterinarian for an examination and some diagnostic testing. The suggestions I gave you may give her some relief, but I am concerned that she is really sick.
Please let me know if you have any further questions.