Could my mental health issues in part be caused by attending a whacko Catholic school?

Hard to say without details. Is the religious aspect of your school causing you significant stress?

How we are as kids can change the way we are as adults. I have problems to

being alive for long causes mental issues too

Probably!

What would you define as a "whacko" Catholic school?

Could be this guy too.
[image deleted]

Depends on your issues. But it's entirely possible. Christianity tends to instill feelings of being unworthy wretches that are made valuable only through the love of God. That can definitely hit the psyche pretty hard.