If you get really bad, have a temperature or obvious sinus/chest infection do go to the docs. I got put on antibiotics last week after a week of trying to keep what a thought was a cold at bay with paracetamol & honey/lemon drinks. I ended up with it in my chest and sinuses so it could have been flu.
The doctor said I probably should have seen him earlier as its better to get well quickly than try and fight it off if your immune system can't cope. Whilst the antibiotics don't remove the cold/flu, they did clear the infection which then helped me start to shift it. It's weird that you can't take most common cold remedies but can have antibiotics - though I said that to my DH (who studied chemistry) and he laughed at me!