I am very sorry to hear about Apollo's lack of appetite this morning, eating and vomiting plant material and loose, dark stools.
Vomiting, lack of appetite and soft stools can be related to something as simple as a quick change in diet or treats or getting into something he should not have like the garbage, a bug, plant material or a toxin. More serious causes are viral or bacterial infections, gastrointestinal parasites including worms and protozoal parasites, pancreatitis, a dietary allergy or sensitivity, inflammatory bowel disease, internal organ failure, a full or partial gastrointestinal obstruction or even infiltrative cancers like lymphoma (less likely at his young age).
Dogs with nausea or gastroesophageal acid reflux often eat plant or foreign material to make themselves vomit. They will often swallow repeatedly and lick things trying to soothe their nausea and acid burn. If they can rid themselves of whatever is irritating their stomach that way then all is good. But when they are vomiting repeatedly and continue to be uncomfortable then we need to stop them from eating any more grass. It becomes a vicious cycle where the more they vomit the more their stomach acid burns their esophagus and the worse they feel.
Dark/black liquid or tarry stools usually indicate digested blood in the stool.
Bleeding can be caused by a primary viral, bacterial or protozoan infection, or eating something that irritates the gastrointestinal tract, inflammatory bowel disease or a severe case of parasites, an obstruction or twisting of the bowel leading to intestinal wall damage, internal organ failure or cancer.
The danger with blood in the stool is that means the intestine is raw and a raw intestine more easily allows bacteria into the abdominal cavity itself and can lead to peritonitis. The darker color of his stool indicates the blood is in his stool is from farther forward in the intestinal tract.
Can you check his rectal temperature for me? Normal dog temp is 102F. A fever is >103.5F.
Can you also check his mucous membrane (gum) color? They should be bubblegum pink and if you press on them they should blanche then return to pink in less than 2 seconds. They should also be moist not sticky. If they are sticky that means he is dehydrated.
If his color is fine and he doesn't have a fever or a subnormal temperature (less than 99F) then he is more stable than a dog with a high fever or a low temperature, but I still would recommend an emergency examination today given his age and symptoms and the length of time that he's been sick.
If he has a fever, his mucous membranes aren't pink, and when you press on his abdomen it seems very tense or painful I would be more even concerned. These are signs of a blockage, pancreatitis (inflammation of his pancreas causing increased enzyme production, usually related to a high fat meal) or possibly a viral infection. These are emergency situations and he needs to be seen immediately.
Is your fellow current on his vaccines?
Does he go to dog parks or doggie daycare or has he recently been boarded?
Is he a pup that likes to chew on and ingest things he shouldn't?
If there is no way to have him examined immediately there are a few things we can try, but I would recommend observing him very, very closely today.
To try and settle his stomach today you can give either:
1) Pepcid-ac (famotidine) at a dose of one half of a 10mg tablet per 10 to 20 pounds of body weight 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.
These will reduce stomach acid and should help if this is related to simple nausea and gastrointestinal irritation. These medications can be used for a few days as needed as they are quite safe.
I would not feed him any food for 6 hours after the acid reducers are started.
This should help stop gut spasms and restore normal gut motility. Small amounts of water or ice cubes given frequently are fine as he needs fluids after all that he has lost with vomiting and diarrhea. You can give him pedialyte to replace electrolytes too but Gatorade is much too high in sugar which can make his intestinal irritation worse. Do not allow him drink too much at any one time as that can lead to vomiting.
Today even with the fast a couple hours after the acid reducers you can start Kao-pectate at 1/2ml per pound or 1/2 tablespoon per 15 pounds of body weight every 12 hours. This will coat his irritated gastrointestinal tract as well as absorbing bacterial toxins. You can use it for a few days until his stools look normal. You can find kao-pectate at the drug store.
After his food fast start a bland diet of 1/3 boiled hamburger (or boiled, white, skinless chicken), all fats and juices drained off the meat, mixed with 2/3 boiled, plain white rice, add 1 tablespoons of canned pumpkin (not pie filling, just pumpkin) to each meal. Feed small meals frequently until you figure out that it is sitting well with him, then gradually increase the amount and decrease meal frequency. I would start with 1/4 cup for the first meal.
Once he feels better (no vomiting or looses stools for 48 hours) start mixing in his regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert her back.
Well worth checking at least a couple fresh stool samples too even if he seems to improve as parasite eggs/cysts are common in puppies and are shed intermittently, so they may be picked up on the second sample or third test even if the first is negative.
If he has a tense painful abdomen, continues to vomit even with the acid reducers, becomes very lethargic, or runs a fever greater than 103.5F then he really must be seen by a veterinarian as soon as possible on an emergency basis as anything you give him orally will just come back up worsening his dehydration.
Please let me know if you have any further questions.