That could be migraine. It wouldn't be my first thought, but it wasn't your doctors first thought either. Nausea is very common with migraines, and vomiting is not uncommon. It's also possible to have a migraine without the headache pain part of it. Migraines being a whole cluster of symptoms, you can have a migraine with any particular symptom being absent.

If that is what you have, I hope it will respond to migraine drugs.