People often think they have flu when in fact they just have a bad cold, as some of the symptoms are the same, especially in the early stages. They both often start with a cough and a sore throat, and with severe colds there can be flu-like symptoms such as a mild fever. However, they are caused by different viruses and actually are different illnesses.

If you have a runny nose and sneeze a lot it's likely to be a cold, even if you also feel tired and have a headache. You should start to feel better after a few days or a week.

With flu, you may have a high temperature and you won't just feel tired: you feel so tired you can hardly move, and you have aches all over your body. If you feel you can't even climb the stairs and everything aches, even your fingers, that's flu; and if you've had it once, you will never confuse the two again.

You can find more exact information about the symptoms here.