What just happened?

This is so weird and I'm freaking out!

My 3 month old has been sleeping through the bight (8-10 hours) for about a month. I put him down around 8:30 and usually pump another 2oz around 11. When he wakes up at around 5, he feeds on one side and I pump on the other - usually about 4-5oz. This morning when he woke up I followed our usual routine, but literally nothing came out with the pump! (The pump isn't malfunctioning)

Is it possible for milk to stop so suddenly? I'm pretty sure there was plenty on the other side because baby is fast asleep again after 10 min on that boob. I had a clogged duct on the empty side yesterday, so maybe that's the cause? Idk why it would be because I had plenty of milk on that side just 5 hours ago!!!

Has this happened to anyone? Will it be better tomorrow? Help!!

Update: in case it's relevant, I exclusively breast feed and am only pumping because I want to build up supply for an upcoming work trip.