The common cold is the name used to describe a simple upper respiratory tract infection (URI). The symptoms of a URI include a runny nose, a cough, feeling run down, and sometimes a low grade fever
. In people that have a normal immune system, the symptoms should not last much more than 2 weeks. Since your symptoms have been going on fro 3 weeks, and you are feeling nauseous, then I would question whether or not you really have a cold. Another possibility is that you have a viral bronchitis
. This is like a cold, but the infection runs a bit deeper into your lungs and can last 3 to 4 weeks. The primary symptom of viral bronchitis is a cough, though a runny nose is also common. Vomiting can occur as well, but this is usually caused by a really long coughing spell (you cough a bunch then vomit). If you are feeling nauseous without coughing, then you likely have something else going on.
I suggest that you schedule an appointment with your primary care physician
. He or she can listen to your symptoms and perform a thorough physical exam. This may be all that is needed to make a diagnosis and begin the appropriate treatment.