When shall I be concerned, is it a common cold or something worse?

GO SEE A DOCTOR. If it has been going on for two weeks you are WAY past the time of even self diagnosing. There can be a lot of reasons for this, it’s probably flu gone bad, but in any case GET CHECKED OUT.

Go to the doctor, it sounds too bad to just blow your nose and go back to school, go to a doctor and he’ll send you priscription so it’ll heal, but until xmas, stay in your bed, take a hot water bottle in with you and just stay in bed, tired or not, stay in your bed, call your mum up to take you any drinks or food, if you have a sore throat, don’t talk, it may get worse until you see the doctor, so listen closely, stay in bed, hot water bottle, you can read to take your mind off things (that’s normally what I do) and just stay in bed really until you see the doctor, if you’re feeling sick when you stand up, before you go into the car, get your mum or dad to help you up, drink lots and lots of water! that’s what my friend did when she wa sick. good luck and hope u’re feeling better beofre xmas!