I had very similar issues to you. At school i was 1st set for everything and top of the class in most of my subjects.
Unfortunately, just as with yourself, i hit some major problems in my life. At 15 i dropped out of school.
I did take my GCSE's but only managed to get a C in Maths and D's in Science & History. The other grades were E's and below.
Obviously these grades weren't good enough for me to progress to A-level so i decided to study at a lower level at my local college. Business & IT i think it was.
This turned out to be a mistake as i was no way near ready to throw myself back into full time education. After a few months i had dropped out and went and got a job washing dishes at a large city center restaurant.
After a year or so of this, i decided it was finally time to ease myself back into education. I enrolled on a GCSE English night course at my local college, once a week for a year while still working in the restaurant.
The following year i decided i was ready to take a step further and enrolled on a mature access course. This was tough, and after a few months i knew that i still wasn't fully ready. Despite that i battled on and finally completed the course. I received several offers from some very well respected universities also.
I turned these offers down and chose to continue working for a few years, as i really felt that i wasn't quite ready for uni and it would turn out to be a very expensive mistake. I worked my way up the ladder at my restaurant and eventually became the head chef. Despite working nasty hours, i was actually making reasonable money, especially for someone my age.
It was at this point that i decided i was ready for university. I applied, and was accepted down in sheffield to do Digital Media Production. I'm now 23.
Basically what i'm trying to say, (sorry about the life story), is take your time, dont rush things. Most people go thru bad times in their lives. Unfortunately for you and i, it was at probably at the worst time. This doesn't mean that your life is over.
Don't feel pressured to do things the way everyone else does GCSE->A-level->Uni.
Every body is different and for some people these things take more time.
I had people putting me down, telling me i was useless, good for nothing. Thats what drives me now, it is my goal to prove these people wrong. And being honest, to prove to myself that i am capable of great things.
The most important peice of advice i can give to you is - make sure you'r always doing something. Be it college, a job, or both. If you allow yourself to stop, it can be a slippery slope and you will find it very hard to activate yourself again. Oh, and stay away from dope
Good luck!