milk supply decreased :(

I'm breastfeeding/pumping for my 5week old son. My first milk of the day I could pump 10oz from both breasts and 4-7oz throughout the day after or 2oz after a feeding. Now after a feeding I'm dry and if I only pump can get only 3oz from both breasts together. Idk why my milk supply has been cut so drastically overnight (3 days ago) and I'm digging into freezer stash just so my boy is fed. Trying pumping for 20 minutes every 2-3 hours but it is exhausting. Also drinking more fluids and eating oatmeal/granola. Why is this happening? Has this happened to any of you ladies? What did y'all do to get your milk supply back up? Thanks in advance. 🍼💙