Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear about your girl Lily's loose stools and vomiting.
Does she have blood and/or mucous in her stools?
Has she vomited any more today?
The important factor in all of this is how your girl feels otherwise. If she still has somewhat of an appetite and isn't lethargic then that is a good sign. If she is very lethargic and has no appetite, and is unable to keep anything down, even water, I am much more concerned.
Vomiting and diarrhea can be due to stress, a change in diet, eating something they should not (like sticks or other plant material outside), parasites, a viral or bacterial infection, metabolic organ disease, inflammatory bowel disease or even a food allergy.
Since this started with vomiting and now is progressing to diarrhea that indicates some sort of irritant that is making its way through her gastrointestinal tract. I would be highly suspicious of her eating something she should not have or a viral or bacterial infection.
She should improve with the recommendations I give you over the next 2 to 3 days. If not she should be checked by her regular veterinarian. Well worth checking at least a couple fresh stool samples too as parasite eggs/cysts are shed intermittently and they may be picked up on the second sample or third test if the first is negative.
If she still feels pretty well now though we can try some things at home.
Since she has some stomach upset and reflux to go along with her loose stools to try and settle her stomach today you can try 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 half of a 10mg 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.
I would not feed her any food for 12-24 hours. This should help stop gut spasms and restore normal gut motility. Small amounts of water or ice cubes given frequently are fine as she needs fluids after all that she has lost with vomiting and loose stools. You can give her pedialyte to replace electrolytes too but Gatorade is much too high in sugar which can make her gastrointestinal irritation worse.
Today even with the fast a couple hours after the acid reducer is given if she is no longer vomiting you can start Kao-pectate at 1ml per pound or 1 tablespoon per 15 pounds of body weight every 6 to 8 hours. This is quite safe and will coat her irritated gastrointestinal tract as well as absorbing bacterial toxins. You can use it for several days until her stools look normal. You can find kao-pectate at the drug store. I like the kao-pectate formulation with kaolin and pectin better then Pepto Bismol as Pepto has salicylates which are in the same family as aspirin, and can further irritate the intestines.
If she has a tense painful abdomen, continues to have diarrhea with no improvement after being on kao pectate for 24 hours, becomes very lethargic, begins vomiting again, or runs a fever greater than 103.5F then she really must be seen by a veterinarian as soon as possible. Make sure to take a fresh stool sample with you when you go.
After her food fast start a bland diet of 1/3 boiled, lean hamburger (or boiled, white skinless chicken), all fats and juices drained off the meat, mixed with 2/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 1-2 tablespoon of canned pumpkin to each meal if she has mucous or blood in her stool as fiber helps soothe an irritated colon. Probiotics such as Fortiflora, Proviable, or Benebac can be added to the bland diet mix to help replace appropriate bacteria.
Once she feels better (no diarrhea or vomiting for 48 hours) start mixing in her regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert her back.
If your pup is feeling very lethargic and continues vomiting though it would be best that she see a veterinarian now as anything you give her orally will just come back up worsening her dehydration.
Best of luck with your pup, please let me know if you have any further questions.