The yellow phlegm in the morning indicates that you most likely have a chronic sinus infection, which can go on forever. You are on the right track, with the saline, but squirting it up your nose is semi-useless due to gravity. I invented a technique to defeat gravity, which makes it possible to wash the infection out of your upper sinuses, which will cure the problem.
http://www.medhelp.org/user_journals/show/2322
It's risky, because you have to bend over in a shower, but you can also do it outside in swimwear, and anyway you are young. Keep doing it for at least 3 days after the symptoms go away to keep it from growing back.