It sounds like your dog has Vestibular Disease. Common signs are: ataxia (incoordination), head tilt, nystagmus (rapid eye movement), nausea and vomiting.
1. Old dog Vestibular- unknown cause most commonly. These are older dogs and signs will have a sudden onset then get better and normalize over 1-2 weeks.
Stem tumor- less common, signs will continue to get worse over a few days and usually progress to seizures
. The only way to differentiate is with an MRI which is often not done since most dogs will recover from the old dog vestibular.
Meclizine (Antivert)- this is an anti-motion sickness drug most commonly used. I give 25 mg per dog once daily for 7-10 days. It may be over the counter so you can call your pharmacy and see if they have it.
Midazolam- valium type drug that I give an injection of once to help with the anxiety and it seems to resolve the signs a little faster.
While it's scary at first, most dogs with Vestibular disease will have a full recovery. You have to be patient and understand it can take up to 1-2 weeks. Good nursing care- bringing food/ water to her, keeping her from stairs, helping her to walk outside, keeping urine off her if she urinates where she lies- is key to these cases.
I would either go to an ER vet tonight for the meds or get her to your vet in the morning and get her started. The antibiotics are not likely to help here.
I hope this helps, let me know if you have any other questions.