Nipple pain at 4 mo

CiCi

Hello! I was hoping to get some advice. My son is four months old and exclusively breastfed. He is my second child and this is my first real go at breastfeeding. Things were really going well until recently when we had his four month check up. He went from 50% to 7% in terms of weight. He is 45% in terms of weight. Ladies, he breastfeeds ALL the time...I am a little worn out even from it especially bc of my first child who is 3yr and very active. My nipples actually hurt. They have been sore for probably two weeks now...not cracked or bleeding. The doctor recommended giving him some rice cereal mixed with milk or formula. I guess I am wondering if anyone has any advice or this has happened with the sore nipples later on?