Mamas who have had their babies.

Does your baby have lumps under their nipples? My son is almost 3 weeks and I've noticed a hard large lump under his nipple area on the left side. The right side also has it but its not as large. It totally freaked me out! I googled it and everything that i am reading is saying its normal for baby boys and girls. And that it is a hormone that is passed on from the mom.and that with breastfed babies its more noticeable.I was just curious just how common it is? And how long wete the lumps there?