Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your pup Moss is not eating for 2 days, vomiting, has diarrhea, and is lethargic after eating an unknown number of cherries 3 days ago.
Drooling indicates nausea.
There are a couple concerns with cherries and their pits.
The first is that the pits do contain small amounts of cyanide. But the amount in each pit is very small and if the pits aren't cracked open the cyanide cannot be absorbed. So unless he chewed on the pits and cracked open a huge amount of pits then cyanide toxicity is very unlikely.
The second concern is that if he ate enough of them they can cause a blockage.
Finally eating a large amount fruit can cause gastrointestinal upset.
These may pass but since he is vomiting and has diarrhea I am concerned.
To try and settle his stomach tonight 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. (3 of the 10mg tabs every 12 hours for him)
2) Prilosec (omeprazole) at a dose of one 20mg tablet per 40 to 80 pounds of body weight every 24 hours. (2 of the 20mg tabs every 24 hours for him)
These will reduce stomach acid and may help settle his stomach. These can be given for several days if need be.
I would wait a few hours to try to offer food.
If he stops vomiting then feed a homemade diet of 1/3 boiled, lean hamburger or boiled, white, skinless chicken, all fats and juices drained off the meat, and 2/3 boiled, plain, white rice. Add 2-3 tablespoons of canned pumpkin, (not pie filling, just pumpkin), to each meal for fiber to help push the remaining pits through.
In most cases cherry pits do not create a problem because they are fairly small, but perhaps he ate something else that you are unaware of.
If he continues or stops and then restarts vomiting, has a tense painful belly or refuses to eat even after the acid reducer is given, or runs a fever (more than 103F rectally) then that can signify a blockage and he should be seen by a veterinarian immediately.
Surgery may be needed at that point.
Please let me know if you have any further questions.