history: I'm a bit nervous- I have an upcoming certification exam to take for my teaching license and it's a big deal. I'm a bit nervous- I have an upcoming certification exam to take for my teaching license and it's a big deal.
current: That's an amazing accomplishment!  I'm sure you'll do great!  Have you been studying a lot?
next: I've been studying a WHOLE lot - so I think I'll do okay, but it's still making me feel nervous.