Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Lulu has had two episodes of vomiting in the last two days, is sneezing and has a runny nose. I am glad to hear that she seems to feel well otherwise.
In many cases vomiting is triggered by eating something they should not, too much table food, too many treats or something they find outdoors, esophageal reflux, or a dietary allergy or sensitivity.
More serious causes of vomiting include viral or bacterial infections, chronic pancreatitis, inflammatory bowel disease, internal organ failure (kidney or liver disease), a full or partial gastrointestinal obstruction or even infiltrative cancers such as lymphoma. She's a young dog and seems well otherwise, so these causes seem less likely.
Her runny nose and sneezing may be due to reflux into her nose irritating her nasal passages. Or it may be that post nasal drip may lead to some nausea.
Being that she feels well otherwise, you might be able to try some things at home and take a wait and see approach. But because this is the second time this week if this continues we need to take this a little more seriously and look for an underlying cause.
Rarely a parasite called a stomach worm (Physaloptera) can lead to intermittent vomiting. These are difficult to diagnose because they rarely shed eggs, so we can try simply worming her with a gentle wormer called Pyrantel and see if that helps. This is easy to do and inexpensive so well worth trying once we get this episode of vomiting under control.
Some dogs seem to vomit more on an empty stomach so feeding her small meals several times a day, and maybe a snack before bedtime, may be very helpful.
It may also be helpful to put her on an acid reducing medication as too much stomach acid, especially on an empty stomach, is very irritating and predisposes to vomiting.
I recommend giving her a dose before bed so that it is in her system in the morning. You can give either:
1) Pepcid ac (famotidine) at a dose of ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of ¼ of a 20mg tablet per 10 to 20 pounds of body weight every 24 hours
These are both acid reducers and should help her feel better. They are quite safe and can be used long term if necessary.
You might also consider feeding a low residue, low irritant easy to digest food if this becomes a repeated problem for her. Both Science Diet and Royal Canin make sensitive stomach formulas.
If her sneezing and runny nose worsen, she runs a fever, and/or starts coughing then she should see her veterinarian.
If she continues to vomit even with the acid reducers, runs a fever (more than 103F rectally), has a tense painful belly or if she refuses to eat she should see a veterinarian for an examination, and some diagnostic testing. I would start with a complete blood count and biochemistry profile, a specific test for pancreatitis called canine specific pancreatic lipase, as well as fecal checks for parasites. She may also need an abdominal ultrasound to look into this further if we suspect a possible foreign body.
Please let me know if you have other details or a particular question based upon my response.