1 1/2 months old

So my baby boy finally had his one month check at 1 1/2 months and he only weighs 9lb 12oz and is 22 1/2 inches long. When I weighed him at home on the scale with me at 1 month he was 10lb 3 oz. I brought this up to the Dr so she looked at the charts and he is falling off his curve. I’m freaking out. I told her too that he has a hard time eating all morning and won’t eat well till like noon. In the mornings it’s hard to get 2 oz into him. So she brought up changing his formula to nutramigen…. Well my son is already on nutramigen formula. So now I have to go in again in another 2 weeks to check his weight. I’m freaking out cause I don’t know what to do to get him to gain weight or get him to eat in the mornings. He takes in anywhere between 14 to 16 oz in 24 hr period. The only other formula I can put him on that doesn’t have the cow Protein in it is Alimentum. Has any other moms experienced there babies not gaining weight on nutramigen? He is also known as a happy spitter. (Tried medication and it did nothing for him)