Baby not gaining weight

Alyse

DS is 5 months old today and hasn't gained any weight in 12 days. He is eating like normal during the day and eats 25-30 oz breastmilk on days I work and can't breastfeed. I called the pediatriction but I'm waiting for a call back. No puking, diarrhea or fever. I have an at home scale and he hasn't gained (or lost) any weight since he was weighed last (at the peds office) 12 days ago. He is fed exclusively breastmilk. Has anyone else had this problem??