I don't have more than ten friends

As a 24 year old I find this a weird statement, and the only thing I can say is that you need to create a strong/stronger bond with your better friends in this group, because when you're 20, 21, 22 etc 10 friends is A LOT. When you start work or get into a new hobby you'll meet new people and gain acquaintances but most people will only have a couple of real friends, so this really isn't an issue providing you have at least one true friend that will be your rock.

I don't do well in school.i feel like I burden my family and the people around me

Why? Do you put off studying to do other shit? Why do you feel like a burden on your family/friends?

If you CAN do something about it (i.e study more, get a part time job, do some chores etc) then do it. Helping other people can be such a good way to make yourself feel better, even if it's at the expense of your time or effort. If you can't do anything about it then it's out of your hands and you need to try your best to forget about it, because if you can't control it then it's not worth getting upset over.

When I even attempt to talk to my friends about it, the conversation always sways their way and we end up talking about their troubles, what they're stressing about.

This just shows that a) everyone has something to worry about and b) most people think what they're going through is the most important thing. From this you need to take away that you might be feeling really shit, a little bit shit, I don't know, but there are lots of other people feeling the same so it's not just you.

Your sister is just being a sister. Until you're both adults and move past this kind of stuff it's rarely going to be a serious type relationship, in my opinion.

If you need someone to talk to drop me a PM