I am having a blocked nose for 3 weeks now, help me?

About 3 weeks ago, i felt my nose was all blocked up for a large part of the day, expecting a cold i never paid heed. Since i have a adenoid problem since childhood- bad colds, a terribly blocked nose and even ear infections with fever were never uncommon to me, but now i am 17 years of age and the incidence of these had reduced greatly. But this time- I felt something was not right when i didn't have a cold for a week and no other symptoms other than a blocked nose.But about 6-7 days back i experienced a headache that wouldn't go". I went to a reputed doctor and told him about what had happened but surprisingly he said that even though i did have a blocked nose- my adenoids were not significantly enlarged-so they aren't the problem. I started using a xylometazoline nasal drop about 2-3 times a day and it gives a completely fine and unclogged nose for about 4-5 hrs. after which the stuffiness returns. As for the headache i had and eye-check up and was told that i had a perfect vision but a mild muscle weakness of the eye and was told eye exercises,they also told me to improve my posture as i complained of a stiff neck. With the eye exercises and posture improvement the headache seems to have improved but sometimes it comes back and i think it might have something to do with my blocked nose- like a sinus problem. I am also suspecting an allergy problem- THOUGH I HAVE NEVER BEEN ALLERGIC TO ANYTHING ALL THESE YEARS. I don't have any fever, coughing or sneezing. But sometimes i feel as if there is thick slime in my throat and i try to swallow it down-what is it?