My pediatrician freaked me out a little

I brought my daughter for her 15 month visit today. at her 12 month, her weight was 21 pounds 6 oz, her height was 28.25 in, and her head was 45 cm. Today at 15 months, her weight was 21 pounds 14 oz, her height was 30.5 in, and her head was 45.5 cm. He said he was concerned about her weight gain and wants to see her back halfway between her 18 month visit for a weight check? Should I be concerned? I was impressed she grew over 2 inches and all happy and then he dropped that on me. I thought it was normal for them to level out once they’re off formula? He even suggested giving her formula again which I thought seemed weird, especially with the shortage, I can’t imagine taking the limited supply from 2 month olds…