chronic dry coughs wear me out and make me tired.

Hi there, im writing here because of my utmost frustration at being able to find a solution to my chronic cough. i am a 24 year old male relatively thin weighing only at 120lbs and being 5'11 tall. my health record is generally good with no serious health problems. only thing i can think of is minor heart murmer. I do NOT smoke nor do any drugs. none of my relatives or friends do either. i live in a clean environment and regular commute to college with my vehicle. i do not work anywhere with bad weather. Starting 3-4 years ago i started having these dry hacking coughs that lasted for about 3 months. i saw a specialist and he said i have 100 days cough which comes and goes and that there is nothing i can do about it. it used to be that i would get this once a year with last time being in june 2011. None of the doctors that i have ever seen been able to help me. Anyway i started coughing again since last week only 7 months after it stopped. it seems the period between these coughs is getting closer in time. i am very worried as these coughs really wear me out and make me tired.

The symptoms:
- dry hacking cough specially in cold dry air
- tickling sensation in throat
- most of the time when i lie down it goes away
- i do not cough while sleeping
- NO cough or allergy medicine helps
- inhaling hot steam helps stop coughs (near a humidifier)
- drinking hot tea/coffee temporarily stops coughs

please if anybody have any idea what i'm suffering from and how i can stop it from ruining my education and life, it will be appreciated. thanks.