At Insight, we completely understand how you are feeling and want to reassure you that you are not alone when you have these feelings.
But here's the first and last advice: stop listening to advice!
The only person you should listen to is yourself. Below we have outlines the steps you should take in your path to self direction:

Start with YOUR INTERESTS:
Reflect i.e. spend some time reflecting on what you enjoy, what you do not enjoy, your aspirations from life, your life goals. Use reflective tools like this Personality Test to get you going:
Now, plan on engagements to Discover their features i.e. do you actually like what you think you like? Can you spend hours and hours doing that thing? Hone in, on exactly what you like. This exploration can not happen through reflection. We encourage you to go out into the world and test your Interests.
SKILLS:
Now that you have a rough idea of where your interests lie, build a career plan around your interest. Now you need to do Research. Ask professionals, google, career databases, find as much as you can about the career that seems to match your interest to help you make informed decisions. 
Develop a plan to build skills needed in those fields. Internships, academic degrees, online seminars, use what you have found during your research to build skills. 

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​There is no easy answer to your situation.  You sound like you are capable of studying science.  But you are not interested in it.  Did you used to be interested and you lost your interest?  Or, you are someone who is not really interested in any subject, but can study well anyway.  I would say it is not possible to guide what is a good solution until we have more information on what you ARE interested in, not only that you are NOT INTERESTED in science.  If you don’t study science, what will you study?
I might be giving you the oldest philosophical advice when I say “Know yourself.”  If you do not know your interests and skills, you cannot give a good direction to your life.  And if you cannot give that direction, someone else will!    So, you can to give attention to the process of learning about yourself, not just about subject they teach in school.
At Insight, we advise students a simple model of self-discovery: reflect >engage >repeat. Reflect on your interests, what makes you happy, when have you been touched by an intense emotion?  You can , ask your parents, your friends, your siblings about their thoughts.  But reflection is not enough, you must get out of your head and enter the world.  Engage in some activity that you are interested in.  Really take part and to discover how you feel.  Did your interest increase or wane?  Now, you are reflecting.   This back and forth between action and reflection will help you better understand yourself.
Then, you would know what to do.  It is said, "Not having a plan, puts you at the mercy of those who do have one." If you know who you are, you will know what to do, and you will no longer be at the mercy of other people telling you what to do.

​No. In fact computer classes and language classes can be useful.  But you should ask yourself are you really interested? Or are you going because your friends are going?
A lot of students take bridge courses after their SLC just because that is what everyone does. Parents are happy that their kids are 'studying'.  Bridge course institutes are happy that your parents are paying the fees, and you are happy as you feel you are not just sitting home doing nothing.  Many students do not take bridge courses seriously.  They mostly bunk those classes and go to the classes just to ‘kill time’ and to hang out with friends.  You don’t lose much by going, right?  After all, the course material in these courses will be parts that you have already studied or will naturally study later in high school.   So, you just go, what’s the harm?
If you are going just because everyone else is going, and you do not know if you are really interested in the course being taught, I would highly discourage you from joining bridge courses.   Sure, you need to prepare for what comes next in your life.  You should do research on your own, or with a group of friends.  All that is useful because you are an active learner in those classes.  In bridge courses, you just take in passively what is taught to you.  This may teach you a bad habit.
In conclusion, bridge courses are useful only if you have an active interest in the course.  If not, you are better of finding a more productive way of using your time.