Sometimes they call me "Sunny" because I'm a very soft person and try to stay positive in every situation. Sometimes they call me "Sunny" because I'm a very soft person and try to stay positive in every situation.

You need an article in front of a noun.

But I also know that my friends and family have seen my depressived side and they have supported me on my way to becoming a human again. But I also know that my friends and family have seen my depressed side and they have supported me on my way to becoming a human again.

Also I was a straight-A student at school. Also I was a straight-A student at school.

However, at the Uuniversity my grades dropped and my knowledge remained solid only in interesting areas of science. However, at the university my grades dropped and my knowledge remained solid only in interesting areas of science.

You wouldn't capitalize "university" unless it's after a specific name, such as "Cornell University" or "Shanghai University". If you're talking about university in general, it's common to simply say "at university" or "in college".

To me, this is a really difficult question to me. To me, this is a really difficult question.

You generally specific the subject (ex: yourself) at the beginning of a sentence.