When I did my care plans
I never included pain as one of my priority nursing Dx. Unless I was desperate... there is always more to the story. I think of pain and infection as "easy" ways out...
Pain causes pain. There are cases wher pain can cause more harm, such as prevention of deep breathing, thus causing PNA, or prevention of ambulation, thus causing a dvt.
Nausea and vomiting affects acid base balances, can cause dehydration, possible aspiration, nutritional imbalances, etc.
Between the two, I'd pick nausea/vomiting as a much higher priority.
What's causing the pain and nausea??? Focus on that. Obstruction, Disease processes, bleeding ulcer, gallbladder...etc