K.M.
Hello I.,
This may get confusing seeing recommendations to apply heat and then others that recommend cold...
What I used to do when I had this type of problem is to apply Quark, which is something like strained cottage cheese, nicely cool from the fridge. I'd put it on a washing cloth or another type of cloth that wouldn't allow much liquid to drain through like "spitting cloth for babies" and keep it on over night, exchange when it gets warm and wipe off with water and mild soap before breastfeeding.
The Quark/Strained Cottage Cheese has multiple effects: It cools, it has a high mineral content and is acidic, which promotes healing and diminishes the swelling.
There is homeopathics, too, like Bryonia in 6X or 30X which you can take following directions.
You can find quark in health food stores, cottage cheese may work, too.
Good Luck! K.