Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry that you have been waiting for a response, but your requested expert isn't online which delayed your question coming up on the list for all to answer. I would like to help if you are still interested in an opinion.
I am sorry to hear that your fellow isn't feeling himself, with episodes of vomiting and diarrhea with grass in it, and increased noise from his stomach.
These noises are the result of ingesta moving through the gastrointestinal tract and gas bubbles. In most cases they are completely normal and seem to cause the dog no distress. But in cases where the dog acts uncomfortable and is vomiting and/or has diarrhea it is likely that the pup is experiencing some reflux or abnormal motility, or painful intestinal spasms that are more than the usual. In severe cases this can be linked to pancreatitis which is a painful inflammation of the pancreas leading to increased enzyme leakage.
Possible causes include a change in diet, dietary sensitivities or allergies, or eating things that they should not like too many fatty table scraps or garbage, bones etc, or a viral or bacterial infection. Metabolic organ failures (kidney or liver disease), Addison's disease (hypoadrenocortisim), pancreatitis, inflammatory bowel disease or even infiltrative cancers (less likely at this age) are other possible causes.
I would be concerned most about food sensitivities/allergies, him eating a foreign body or a viral or bacterial infection at his young age.
Has he been fed anything different or gotten into anything different that you know of?
To help with gastrointestinal upset and reflux you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 24 hours
These are acid reducers and should help him feel more comfortable. They are quite safe and can be used for a few days if needed. In some cases dogs remain on them long term if this is a repeated problem.
I would pick up all food for now and water for a couple hours to allow his stomach to settle after the acid reducers. In a couple hours when you give him water or low salt clear broths like low salt beef or chicken broth to drink make sure it is in small amounts only. If he drinks too much too quickly that can lead to nausea and vomiting. To get some electrolytes in you can also offer him a 50:50 mix of pedialyte and water.
If he seems to feel better tonight then offer a bland diet mix of 1/3 boiled, minced, white, skinless chicken or boiled, lean hamburger and 2/3 boiled, plain, white rice or pasta mixed with some low salt chicken or beef broth to make it easy to lap up and swallow as well as increase his fluid intake. If he refuses that you can offer a little meat baby food. Probiotics such as Fortiflora, Proviable, or Benebac can help replace appropriate bacteria. You can add those to the bland diet mix.
If things go well and he does eat and doesn't vomit feed him the bland diet for 2 to 3 days then slowly start to mix back in his regular food, a little more at each meal. It should take about 5 to 7 days to slowly convert him back to his regular diet.
If he continues to vomit, runs a fever (more than 103F rectally), or has bloody diarrhea, especially if he isn't current on his vaccines, or has a tense painful belly then he is not a candidate for home therapy and must see a veterinarian for an examination, diagnostics, injectable anti-nausea drugs intravenous fluids and supportive care.
If you go back to the original food and stop table food and treats and his episodes continue then you may wish to consider using a using a low irritant food, like Hills i/d or Purina Veterinary Diets EN, or a hypoallergenic food such as Hills z/d or Purina Veterinary Diets HA. He may have a dietary allergy or a sensitive stomach.
Please let me know if you have any further questions.