You may have a cold or the flu. If it is accompanied with a fever and general aches, it is most likely the flu. No matter which it is, stay home, drink juice, and get plenty of sleep. Colds and flus are both caused by viruses, so antibiotics will not help.
You could just have a common cold that will go away on its own in a few days. If it is accompanied by a fever it could be the flu. If it becomes severe, you should go to the doctor.
It could be the flu, bronchitis, or a minor respiratory infection. Any persistent cough that doesn't improve after several days calls for a doctor's visit, especially if you also have a fever.
It could be strep throat, the flu, or just a cold. Sometimes having a cough can cause a headache, especially if you are coughing hard or often. It could be the begining of an illness such as a cold.