I am sorry to hear about your results. You do not become a failure just because you failed in one exam. It is a reflection of your interest in the subject. If you are not interested in the subject you can try and talk to your mom about it, share with her about your interests. If you are confused about what to do, list down all your interest areas and write down pros and cons of each, then rate each of them in terms of which will give you long term benefits. One is never 100% sure about a career choice, you select a field and then work passionately towards excelling in that field. Consult a career psychologist or consultant to assess your strengths and weaknesses, your aptitude and select a field accordingly. From what you have described it seems that you are having depressive symptoms, many young adults, people your age have similar feelings and go through similar circumstances. You can overcome these difficulties.

At first decide what you want to be? Then discuss it with your mom. I hope that your mom will understand your problem. Otherwise you can take antidepressants in the morning to decrease your symptoms