Help I'm Losing My Writing Ability

Hello everyone; I don't know if this question is in the right place or not, but I think that most of you would have probably experienced this at one point or another in your life, so do offer some wisdom and advice. However, if the content here is unsuitable, please remove it. Anyways, here's the current situation that I'm facing: * I was able to write very well since young (ever since I begin learning English), and my writing ability was well above the average. My style of writing was considered original and unique to me. * I was able to compose essays and stories very fluidly and improvise plots and arguments in an ad hoc manner. However, this ability has recently deteriorated, and I find myself cracking my head open even for simple arguments and story-lines. * When I wrote in the past, my pen moved almost as fast as the sentence forming in my head. My pen just had a mind of it's own, and I could enter a 'flow' basically 100% all the time. Suddenly everything has become very conscious and artificial. Now, I have to pause and think even about the minutest details, such as sentence structure, words to use, alphabets in the words, etc. * My vocabulary was wide and far-ranging, and I often utilized five to six different words, all synonyms, to re-iterate the same point in an argument. Now, however, my vocabulary has suddenly dropped to one or two simple words. The words used to come naturally, now I have to try to think of it, and most often I cannot. * I used to create very original metaphors and figurative language which my peers and teachers often thought as brilliant and ingenious. I somehow cannot think of anything, AT ALL, now. * I could sensitively appreciate Literature in the past, and often wrote critical essays after reading a novel or story. Also, I leisurely authored essays and short-stories in my free time; now, I find no motivation and lack the necessary 'spark' even if I wanted to. The habit has all of a sudden become very foreign and alien to me. * I'm very distressed with the problem. I can't even list down all the symptoms that I have. I can't describe this psychological torment. It's like whenever I write now I feel it's a chore, whereas in the past it came all natural and flowingly. Thesauruses have become more common and regular in the past few months. The problem has been a recent one, persisting for the past two months already. Here's some other background information for diagnosis: I'm currently 16, and am studying for a national exams at the end of the year. Most of my subjects are very logical and scientific – Physics, Biology, Chemistry, Elementary and Higher Maths – with a few humanities, like English Literature and Geography. A large portion of the education is memory work, except maybe for Literature (and Mathematics, to an extent). My native tongue has been and still is English. The education system in my country is very competitive and quite stressful at times. I'm very agitated by this problem and I want to get to the root of it, which is why I need your help. I want to know how it began and how I should overcome it. I don't know if it's caused by stress, depression or maybe just some other ordinary problem. I'd like to express my gratitude and thanks to whoever offering their help. Writing has always been my passion and a spirited endeavor for me, and I really don't want to see it just disappear overnight. I've been feeling really down these few weeks because of this. Thanks. :)