Top of my boobs are hard. Pumping.

My son is 4 days old. I'm trying to get into the swing of pumping. The top of my boobs are very hard and sore, even after pumping. I read online to apply heat and massage so that's what I'm going to do. I was just wondering if this might be normal when you just start breastfeeding because of all the milk or no? Obviously not normal for ppl who have been breastfeeding a little longer but I was just wondering where I'm just starting if it is. Also feel free to leave and tips or things you wish you had knew about pumping.