I've been feeling more tired and have some cough and fever. when should i see the doctor?

Breathing problems: If you are experiencing cough associated with significant fever, you may very well have pneumonia, and that will require an antibiotic. Most lung inflammations are associated with fatigue, but this is a nonspecific symptom. Other potential causes include a blot clot in the lung, tumor, and other inflammatory conditions of the lung. So, yes, it could be something bad. Best to have it checked out.

Depends: Typical viral infections last 7-10 days and slowly improve over time, but if you symptoms include shortness of breath, chest pain, coughing of blood you should see a doctor immediately.