Going to the vet is the best idea when your dog or cat is sick. But sometimes the condition is such that it is not an emergency and you cannot get an appointment right away. Knowing that there are some medicines that can be used without hurting your dog and might help him or her get through the night or until the next appointment.
For example, Ellie has some itchy skin and we've tried a few home remedies like adding oil to her food and changing foods to get her off wheat. Her itching has persisted so we tried some Benadryl. It's not enough long-term, but it will tide her over until her appointment on Monday. It helped for me to know that the vet had prescribed Benadryl for Sienna in the past, which was another opinion that matched with this flyer I picked up from The Neighborhood Pharmacy.
There are plenty of lists of what NOT to give your dog, but not a lot of what TO give your dog. But here's one.
Calling your vet and getting an opinion on this is probably wise. Repeated vomiting and diarrhea can be severe. Sometimes it's hard to know when it's a real emergency or to wait it out, and you can always call the emergency vet near you for advice.