Nipple pain

My LO is almost 4 months and the last couple of days I've been having pain when he latches and while he is feeding. At first it was just when he would latch on. But now it's almost the entire time he feeds. We did have issues with his latch and worked with a lactation consultant but by the time he was a month old things were going really well. I'm not sure why but it's like he has reverted back to having a shallow latch. Just curious if anyone else has experienced something similar and how to fix it.