How to increase milk supply?

Hi ladies, wondering what could be going on. I’m 1.5 months post partum, no period yet, and my supply has been pretty decent up until probably 2-3 days ago. Before I was able to get 4-5oz all together now I am not even getting 2 oz all together. I made a post the other day about having awful pain but I never stopped pumping and my supply still tanked. I’m horrified to think this is the end of my breastfeeding journey right in the middle of a formula crisis. What could be going on?? What can I do?? I’ve pumped almost constantly today to try and get it to come back. It really doesn’t feel like I’m getting any let downs and my breasts don’t feel like they are getting full like before.