Can't stop thinking about breathing/ Keep needing to take deep breathes?!

We had to do a presentation in school and I got really scared about it before so I tried taking deep breathes to calm myself down, but afterwards I couldn't breathe normally, I have to think about it. It annoyed me all of that night, but I thought It'd be okay and I'd forget it in the morning, but I woke up and was lying in bed then I remembered how I'd been breathing funny and then I started doing it again! Now a week later I'm still doing it. I have to take deep breathes through my mouth or yawn or take a really deep breathe through my nose because I feel as if I'm not getting enough air. It's really really depressing me and I know it's stupid and I should just breathe normally, but I can't! I try to breathe through my nose but then I have to take a really deep breath. It sucks. All I think about now is trying to breathe normally and I've tried so many things to distract myself like going out, watching a film, but then I just remember it again and the vicious cycle begins again!! I also read on the internet other people have had this happen to them but they'd wrote things like 'I started doing that when I was 17 and I'm now 34' I don't want to be like that!! :/ What should I do? I told my Mum and she said 'You just have to re-educate yourself to breathe normally' ...