It's certainly quite common to lose your confidence when mental health problems flare up, whether that's socially, work related or as simple as believing in yourself.

I think I'm just starting to get my confidence back now after it vanished suddenly 2 months ago now...

Hopefully college will help cement it back in place again.

Just take things one step at a time, you'll get there eventually. (metaphorically, not literally talking about the stairs!)