I feel like I made the wrong decision? :(?

Well, I've always loved drawing, and art has always interested me. When I got to secondary school, the time came when I had to choose my subjects for GCSE. I had always thought I'd go for art.. but I didn't. And this was simply because I thought I wasn't good enough. I didn't want to embarrass myself by being the worst in the class. And I guess I kept comparing my work to others. I wasn't even sure what I wanted to do in the future so I chose a mix of subjects... Geography, Spanish, IT and Graphic products. I got B's in them all aside from IT where I got an A. I was disheartened by my B's though as I did try incredibly hard >.> My graphics coursework was one of the best :S But I guess the exam I did brought it down lol. Anyway, the time then came to choose a levels. Ah, I was so confused. I felt as though I should pick sciences... I was good at science... Lol, I did compare myself to others again and did get a tad put off, but i did it anyway this time as I got A's for GCSE in Biology, Chemistry and Maths. So yeah, I chose those for A levels. Including psychology. I do still love to draw though >.< And I guess I figured, something creative wouldn't go with those subjects. Anyway now here I am doing the a levels, and yes I'm finding them so difficult D: I'm not sure if I can even handle the stress, everytime it comes close to exams (like now) I get so tearful with stress, my appetite goes, resulting in less energy, meaning I'm more tired, so less studying >.< My teachers aren't even that supportive.. Since I've moved school I feel like, they only think I'll fail and I feel as though I'd do just that >.> I don't want to have to resit..I really don't :S I'm not sure if I'd be able to take that! Everyone still asks me why didn't I take art :| And thinking about it... I would have enjoyed it so much more.. Well I think so.. I am pretty good at drawing patterns on my nails, both left and right quite neatly.. but I guess I didn't want a profession in nails. Ah, I'm not good at drawing people, but I'm great at cartoons! And I feel more confident about it now . But its too late right? I really don't know what I should do, my future seems so hopeless, and my parents have high hopes for me >.< They don't mind what I do at all, so this pressure I have, is only from myself... Any ideas what on earth to do? I'm 17.