There's nothing wrong in being positive in my opinion. Someone else can't make you positive just by telling you, you have to find it yourself.

On the other hand, if something happens to make you feel better, that can help a lot. For me, it could be stuff like people caring about me out of nowhere. I know it's not the same for everyone.

I'll rate them:

It'll work out eventually--don't worry!

It'll happen when you least expect it!

This person is just trying to cheer you up. Ironically they're correct, if it happens you didn't expect it, that doesn't help though.

People can tell if you're unhappy and it's not attractive!

You need to have a positive attitude!

The person is trying to be helpful but these don't seem very tactful to me.