How to overcome my sickness?

two days ago I woke up to go to school and my throat was dry and it was hard to talk then a few minutes later my throat was sore and filled with a lot of flem. the next day the same thing happened like yesterday, but I also had a stuffy nose and couldn't breathe and I sneezed and coughed. but I still went to school, but I don't know why I went because I felt really tired and my nose was runny. Today I was going to try and go to school, but I am extremely tired and my chest hurts when I sneeze or cough, I can't talk, and I have a headache. how can I overcome this horrible sickness!?!