Redness Of Boob Resulting To Low Supply Of Milk

I pumped my milk for after 9 hours, my breast got engorged and had lumps around the boobs (both right and left. The right boob got empty however, the left boob was not emptied to reserve milk to my LO that night so he could have milk to drink. The next day, I felt pain on my left boob. It's as if parang siyang nabugbog. I hot compressed once it then pumped twice. But I felt it was not emptied and still feel the pain. Same feeling up to now even my LO latched overnight. Any thoughts momsh?