Desperate for Relief for Engorgment :(

This hurts so bad ... I gave birth 4 days ago and all the milk RUSHED in ... I went from a B to. DD in a day and ITS TORTURE ... I can’t not breastfeed because I have cancer ( found out end of pregnancy, it is treatable but still was very scary) I have an ice pack on my breast 24/7 and it kinda helps but it’s just comes back so fast and it hurts soooooo bad ..... any tips to help ? How to slow or stop the milk production ?