Am expressing 40ml at n average evry 2hrs as my son has difficulty latching.my breasts are still very sore.why is it sore and any tips for relief?

Wrong latch: If at all possible, get the help of a lactation consultant. I am almost certain he is just patching to your nipple and not to the whole areola. This causes you to be sore and him to be frustrated because the milk will not let down correctly if he is just getting the tip. There are techniques to show you so he gets the whole area he needs to into his mouth, but someone would need to show you this.