Please don't take this wrong... but it's good that you don't. If you were to dedicate yourself to a "plan", only to find out it didn't fit you later, or you thought you liked it but now can't stand it... what a waste of time!
I don't know about the rest of you, but I'm almost 50 and didn't even begin to know myself until I was in my 20's... and then not really well until I was 30! I say this not to discourage you or anyone else... it's just a fact. Aside from a few basic qualities and tendencies, I resemble nothing of what I was in my teens and early twenties. If I may humbly suggest... start to really identify what you like to do.. I'm not talking "preferences", I'm talking about what you do when no one is around and you loose yourself in the task for hours on end. I'm talking about that thing that if you had food and a home, you'd do it for free for the rest of your life! Then take that 'thing' and look at the 'field' it is in... sounds to me like it's creativity and self expression for you.
Now here is the kicker... do the thing you love... don't stop, but add something new every once in awhile. If you are a writer, try your hand at poetry for a month or so... or write some advertisements for a business or product you know... branch out and try different things.
Keep them in the areas you enjoy, NOT what you excel at unless it is also what you truly enjoy. Reason being it's easy to get trapped at doing what your good at because of the positive feed back... but it may not be your "bliss" (as Joesph Campbell advocated). FYI, it is not only normal to be where you are right now... but the ones with their lives planned out are the aberration and in for a HUGE surprise later.
Keep your options open unless something really "clicks" with you... you'll know IT if and when that happens. Otherwise, channel your studies in the direction of your "things" but not to the exclusion of other less appealing things... chance not only favors the prepared mind, but the well rounded and diverse one as well!
Lastly... there are an abundance of books out there on finding a career or your "gifts". Barbara Sher is a really smart cookie in this area and she has a web presence... check out "Refuse to Choose" and "I Could Do Anything If I Only Knew What It Was". Good reads!
Lastly, be patient... I have an 18 year old son so I know a bit of what I speak... and I was 15 once many, many a moon ago, and yes... I remember very well what it was like.
All my best wishes...