Baby refusing to eat

My daughter is almost 16 weeks old and for the past two almost three weeks she's been refusing to eat. She normally takes 5 oz of formula every four hours but now she's down to 2-3 oz. She acts perfectly happy still, but she's not eating near enough. She has two top teeth getting ready to come in but not cutting through yet, so maybe that is why? It seems like she prefers her paci or gnawing on her hands even if her tummy is rumbling. She's gone from the 30th percentile for weight to the 20th so I get nervous. Any insight would be appreciated.