Tips to boost confidence/self esteem?

I’ve tried positive affirmations and the sort, but they don’t seem to be helping. Suppose I’m looking for something more in the CBT realm. My self esteem is so far in the toilet at this point that it’s severely impairing my schoolwork (e.g, took an exam last week and totally blanked because of how anxious I was), and has long since been affecting the rest of my life. I’m typically one of those people that tend to be pretty good at whatever I try, but my anxiety has just gotten so bad over the last few years, and any time I’m not 100% sure of myself I screw up. Which is only stressing me out more. I’m currently looking for a new therapist, however any tips to tide me over would be very much appreciated.

Thanks in advance!