how long does it take for milk to dry up

I wasn't producing enough and had seen multiple lactation consultants.. I was able to keep up for s good three weeks but unfortunately it's even been recommended to me to switch to formula to make sure she's getting enough. My boobs are KILLING ME and feel like rocks with lumps, nothing helps to relieve the lumps . I tried massaging them and everything with hot pads. I just stopped breastfeeding yesterday ..HELP !!!