Extreme pain

My son is 3 weeks today💙 I started off supplementing, but my milk supply seemed to take a dip so I went to just breastfeeding and pumping afterwards. It always hurt just a little at the latch and then would subside. As of yesterday it began to be painful all through the feeding and my nipples would turn dark purple. Now, it feels like his little mouth is just blades slicing my nipples, to the point where I can’t even stand to let him finish. Is there something I can do? Is this normal? Am I doing something wrong?