Just want to cry (pumping issues)

elduroq9

So for the past week up until today every time I pumped I was getting almost 4 oz every time, and now every time I've pumped today I've been getting under 2 oz, and that's from both breasts combined. This is very frustrating for me because I've been able to store at least three bottles in the fridge and ive had to pump for every bottle my LO has had today. My nipples are sore and I really need some encouragement or advice. Why is my supply suddenly so low today?