Supply suddenly tanked

I've been doing exclusive pumping since about 2 months. It's been okay; my supply is somewhat sensitive and I have to work pretty hard to keep it up. I don't pump at night, which hasn't been an issue. My first pump of the morning I produce 7-10 oz. on average. This morning I produced 7 oz, but every pump since then I've only produced 2 oz!! Normally I'm producing 4-6 oz. Every feeding. I know the power pumping drill to try and get it back up but why would it crash like this?? I'm so frustrated.