Katebabe, I know how you feel - I remember being 15 very well (it was only 7 years ago anyway!). I felt the exact same way when I was your age.
I had always been overweight, and all the other girls were hanging out with boys and making out in the closet at parties and dating and stuff - but no one wanted to date me. I lost the weight, and when I was 14 I had my first kiss... with a 20 year old man. Then I lost my virginity... to a 20 year old man.
Point is, I was so desperate to know that I COULD be wanted by someone that I ended up acting like an idiot and I paid the price for it later.

I wasn't diagnosed until I was 16, and it took a serious event to get me to that point.
I didn't have a boyfriend until I was 15/16, and that was only because I wanted to be wanted by someone - anyone. I broke up with him four months later lol. (I got engaged at 19 btw!)
I also never "fit in" anywhere, despite having all sorts of friends, and everybody at school thought I was a freak.

I wish that somebody had told me when I was 14/15 what I'm about to tell you, 'cause then I'd have time to accept it and maybe I wouldn't have been as stubborn then as I am now.
Never let someone else control how you feel. Don't allow yourself to have your day/week/year ruined because someone doesn't treat you the way you wish they would treat you. Don't let your life evolve around love/finding love/being loved (that's how you get your heart broken); YOU and your friends should be the most important things in your life right now. Don't waste your time trying to "fit in" and be "accepted" - spend your time finding out who you are! To hell with the rest! Don't rush it with boys just because you want to feel loved; QUALITY over quantity girl!
You WILL find a special someone, and NO you won't have to wait until you're 40. He will come, and he will be worth the wait.

Oh and, don't think that your school is the only place you can meet someone. In fact, I'd ignore everyone there (except friends). I never dated anyone from my junior high or high school; those kind of "relationships" are just for show and just for the sake of being with someone - and they end really, really fast.
Get active in your community; I joined the punk scene where I live - it was a lot of fun! Occupying houses, getting surrounded by the police, fighting "the man", meeting hot punk rockers with mowhawks that smelled like beer and vomit... best years of my life! xD
Find out who you are and what you're interested in - and get active.

Being tall is not a problem. I'm fat and it's never been a problem. The only ones who have issues with that are immature teenage boys in your school - who should be ignored 'cause they're really not worth your time. I know plenty of tall girls and it's never been a problem for them either. Out of curiosity, how tall are you? If you are taller than 5'8 you could look into modelling (runway or catalogue) or sports like basketball.
My mom used to tell me whenever I complained about how I could never find any shoes that fit; it's not your feet that are too big, it's the shoes that are too small.
The same goes to you; it's not you who are too tall, it's the others who are too short!

As for the exzema, what kind is it and where on your body is it? Can it be covered with makeup? You should see a dermatologist in my opinion, they can help you with even the toughest skin problems. My mother has sjögrens syndrome, and one of the symptoms is extremely dry eyes and skin. Her eyelids would be red and like sandpaper and she could never wear makeup, and she tried all sorts of products. Then she saw a dermatologist and after a lot of back and forth and testing, he came up with a cream that helped her A LOT; her skin isn't dry anymore and she can wear makeup as much as she wants.
Go for that!

I know this is a long post, but hopefully it helped somewhat. Feel free to PM me!

PS. Trust me on this one, once you get out of high school EVERYTHING will change.