My baby wont gain weight!

Angie
I feed every 2 hour for about 25-40 minutes paced. Earlier today fed him 10 minutes and he gained .4 of an ounce. His birth weight was 7.7 but he had 4 ounce of fluid in his tummy and 4 poops and 1 pee before his first feeding checking out of hospital he was 6.12 pound and has remain 7.0 since last friday now he is 7.1 why isnt he gaining weight?