Feeding -Help!

Liz

So my 10 week old has recently begun eating less, she used to eat 4 oz and and is now only taking 3. She is also taking almost an hour to drink her bottle. She is formula fed. She was born small and struggled to gain weight in the beginning. She is still small for her size. I'm a FTM and don't know if this warrants a call to the pediatrician or not. Any advice?