Why am I always tired?

I'm an 18-year old girl that is relatively fit. I work out for an hour 3-4 times a week, and am active most days. I eat very healthy, and have just recently had a basic blood work-up. I have a slight iron deficiency, which I have had since I was a little child due to a genetic disorder, but I am treating it with supplements, and I also take a daily multivitamin. My other stats are fine, although it was only a simple blood count.

I am always tired, except for late at night. I can sleep 20 hours straight and still feel like staying in bed. Even after getting an adequate amount, it litterally takes every inch of willpower to get out of bed in the morning (or late afternoon, when I don't absolutely have to get up to go to work/school). I even skimp out of social gatherings that are, in my body's eyes, too early. At first I though I was just being lazy, which I'm sure everyone else thinks, but I know that this isn't normal. I am not a lazy person - I was student council president, I'm working two jobs, had perfect grades, ran an NGO for four years, etc. It's just gotten to the point where it can't be my personality. I feel like death every day crawling out of bed, and my sleep schedule always readjusts the longer I leave it to it's natural rhythm. Then, for example when I have to be at work early after a few days of not working, I will just not sleep altogether, so I can get up in time because my waking hours draw out into the early morning. I try, again and again, to get up early and get moving, but I just can't for some reason. I then feel tired, dizzy and gross all day. Then, when I try to go to sleep, even if I woke up at 7am, I'll get tired at around 5pm, but then I will spike at 8pm and only be able to drift off into sleep at 3 or 4 am. This is getting frustrating and I am missing out on life - I can't go to birthday parties, I dread working early and havign to do things early. I am an avid traveler, but have been finding it difficult to visit new areas because I have to get up early, and even after getting 12 hours sleep a night, I have to crash after about 5 or 6 days and sleep for 20+ hours to reload. I can't live my life normally, and I feel like I'm failing. I'm sure everyone else thinks I'm lazy, but that#s just not me! Something is wrong with my sleep.

Thanks so much in advance if you have any ideas. I'm going to book an appointment with my doctor once I get back from a two months stay in Europe, but I was wondering if anyone was experiencing the same or had any ideas as to what it could be. I need answers, because it's truly sucking the life out of me.