Supply decreasing

cassi

So I am almost 4 weeks pp and I was getting around 3-4oz TOTAL each pump. I pump every 2-3 hours. At night sometimes I go 4-5 hours because my alarms don't wake me up. Ever since yesterday I've only been getting around 2oz TOTAL each time.. I also believe I have elastic nipples if that matters. I don't understand why my supply is decreasing