you should! and you must! it may create a health problem in the future! better say it than sorry.
Yes, and I don't think you should be scared of what your parents will say - trust them to help you through this.
yes could be a sinus infection, if your house is dry try boiling water on stove and get all the moisture you can from it! in the winter it gets dry with the heat on so put pots ( old coffee cans) in front or on the heat registers to provide more moisture. but seek help!!! good luck