How long does a stomach virus usually last?
how long are you usually contagious for?
would it be possible to still feel weak and tired for almost a week after nausea and other things end? most important part

On average, it can last 7-10 days while the symptoms can last 2-3 days. You may still feel a little nausea but it wears off as the days go on. If you don't feel the nausea going away, you should contact your doctor, as it could be something much worse than a virus. 

Telling them to either contract or relax