When should you see a doctor if you have cold/flu?

One reason would be. A temp over 104 degrees. Complications resulting from the flu that make it hard to breath is another reason.
Symptoms and timing. Colds and the flu are both viral and we have few antiviral medicines. If you did not have a flu shot, you have higher risk. Flu symptoms progress very quickly and include high fever, severe headache, body ache, extreme fatigue. See a doctor within 72 hours who may prescribe tamiflu (oseltamivir) to shorten the course. For colds, worsening symptoms after 7 days, shortness of breath are reasons for a visit.