Baby not gaining enough weight?

My son is breastfed but is now <1% for weight. He was in the 2%. He’s content after he eats but he still eats all the time (every 1.5-2 hours when with me but every 3 hours when he gets bottles while I’m at work.) He’s 4.5 months old. We supplement while I’m at work because he eats more than what I pump. I pump 11-12 oz and he eats 16 oz while I’m gone.

Do I just have a low supply? We have a weight check at the end of the month. He’s a happy baby and seems content after he eats. I’m just worried about the weight. Thoughts?