Oh dear, sounds like blocked ducts.i had that for when I bf my elder son. what you have been doing are right. Hot compress, continue to bf( if possible, let your baby position such that the nose is pointing towards the hard side) , try pumping as well n keep pressing the area. Cabbage will work quite well to reduce the hardness but b prep that your supple may drop alot after this.
Monitor your temp. If you have fever, pop in panadol plain or see doc. Cos it will have been dev into mastitis. I did a silly thing also. I went on all fours n ask hubby to milk the breast. The gravity supposed to help clear too. Else lie on your side n keep pressing it out.
Blocjed ducts usu happens to pple with oversupply cos you produce more than you can drain out so I think you just have to try to relief it as much as possible.
If all fails, can get a Malay massage lady to help you clear. If want, I can rec you one. She quite good. Hang in there!!